Anatomy, Diagnosis Mechcanics and Management of Anterior Knee Pain

D P Johnson

1 Introduction

Optimum knee function is of vital importance in daily activities and a wide variety of sports. Knee stability is also important especially in running, twisting, jumping and pivoting. Injuries to the knee are very common because of the lack of bony joint congruity and the reliance of the knee on muscular and ligamentous support. Knee injuries are the most common serious injury during sporting activities.

Pain experienced in the front of the knee is commonly described as Anterior Knee Pain. Anterior knee pain affects 29% of adolescent children (Fairbank 1984). This may be related to the increase in structured sporting activity which occurs at school during early adolescence. Anterior knee pain is particularly prevalent in certain sports which include basketball, netball, athletics, skiing and cycling. In these sports, activities are undertaken whilst the knee is in a flexed position, and or jumping is common. To understand the patho-mechanics of anterior knee pain, the anatomy, clinical examination and mechanics of the knee must be well understood. Much of the confusion surrounding anterior knee pain and its treatment has been produced by the inability of the practitioner to translate distinct clinical problems into a specific classification. This applies whether they be a general practitioner or hospital consultant.

2 Functional Anatomy of the Patello-Femoral Joint

The anatomy of the knee can be broadly divided into the three joints; the patello-femoral articulation, the medial and the lateral tibio-femoral joints. To understand the pathology of anterior knee pain this distinction is very important. The weight transfer across the tibio-femoral joint is aided by the menisci which distribute the compressive forces and reduce pressure on any particular point. The patello-femoral joint bears little load whilst standing with the knee in extension. The patello-femoral contact force is greatest between 30 and 70 degrees of knee flexion (Ficat et al). During flexion the site of contact on the patella changes. The area of contact of the patello-femoral joint increases during knee flexion. These mechanisms assist in dissipating the extra loading on the patello-femoral joint during flexion. Nonetheless when descending stairs, jumping or landing as in netball and basketball the compressive load across the patello-femoral joint may reach five times the weight of the body (Ficat et al).

The articular cartilage on the patella is up to 5 mm thick; thicker than anywhere else in the skeleton. Besides allowing unresisted motion the function of the articular cartilage is to help dissipate the compressive forces and prevent excessive loading on the subchondral bone plate. Such pressure is interpreted as pain. Generally it is the extreme forces experienced by the patello-femoral joint during sport that results in the high incidence of anterior knee pain in athletes.

3 Pathomechanics of Anterior Knee Pain

The patella has a very important function in the mechanics of the knee. The patella increases the moment of action of the quadriceps expansion and increases the extensor force by a factor of two to threefold. In the absence of the patella, such as following a patellectomy, the strength of the quadriceps muscle is diminished by at least 30%, the tibio femoral compressive force is increased and degenerative change within the tibio-femoral joint is increased.

4 Anterior Knee Pain as a Symptom

It is important to realise that anterior knee pain is a symptom and not a syndrome. It is insufficient for a clinician to make a diagnosis of anterior knee pain as many different causes have been identified. Whilst it is true that in almost all cases of anterior knee pain an initial period of quadriceps strengthening exercises, physiotherapy and non steroidal anti-inflammatory medication will be prescribed. A provisional pathological diagnosis as to the cause of the pain will give guidance to the physiotherapist, podiatrist, sports trainer and coach. A provisional diagnosis will enable the options for treatment to be discussed with the patient and therapists. The surgical options can be discussed for those cases which do not settle following the initial course of conservative treatment.

To make a provisional diagnosis the clinician should accurately identify the activity which precipitates the pain, the character of the pain and the angle of knee flexion at which the pain is worst. Commonly patello-femoral pain is exacerbated by activities such as descending or ascending stairs, rising out of a chair or driving. These are the activities in which the patello-femoral compressive forces are highest. Any associated clicking, giving way or episodes of patello-femoral instability of the knee should be identified. The exact site of the pain in the front of the knee must be determined, whether it is in the supra-patellar pouch, medial or lateral retinaculum, retro-patellar, at the inferior pole of the patella, medial or lateral part of the fat pad, the anterior horn of the menisci or tibial tuberosity. Thus the history must be detailed and concentrated on the symptoms pertaining to the patello-femoral joint.

5 Clinical Examination in Anterior Knee Pain

Anterior knee pain in athletes may be caused by extraneous problems. In runners and athletes in general, analysis of shoe wear is important. Badly worn shoes or poorly designed shoes may produce excessive foot pronation and exacerbate any tendency to flat feet which may precipitate anterior knee pain. The running or playing surface may also be important, particularly when excessive road running is undertaken. In these cases the pain may be helped by running predominantly on grass rather than on roads. Podiatric advice may be helpful and, despite the reluctance of some clinicians to consider podiatry, it is usually easier, cheaper and painless when compared with operative surgery.

Clinical examination should include examination of the feet, ankles, hips, spine and the contra-lateral knee for stiffness, pain or a clinical deformity. Common clinical pitfalls often missed above the knee are the painful stiff hip, trochanteric bursitis, lumbar stiffness, spondylolysthesis and tight hamstring muscles. Below the knee shin splints, stress fractures, ankle stiffness and flat feet may be related to anterior knee pain. Congenital multiple ligamentous laxity should also be specifically sought as it has a significant effect on the treatment of anterior knee pain.

At the knee the usual examination should be undertaken to exclude meniscal or ligamentous injuries and early arthritis. The range of motion and alignment of the limb in terms of varus and valgus deformity at the knee must be determined. Special attention must be paid to palpate the anterior part of the menisci to exclude an anterior horn meniscal tear. This is best done with the knee in the position of flexion. One should also be aware that both anterior and posterior cruciate ligament injuries may present with anterior knee pain.

Examination of the front of the knee necessarily needs to be detailed and accurate. Inspection may detect swelling as seen with pre-patellar bursitis or Osgood Schlatters disease in which the tibial tuberosity is swollen. An effusion indicates an intra-articular pathology. Palpation should start in the supra-patellar pouch and move down the patellar retinaculum either side of the patella into the fat pad which lies to either side of the patellar tendon. A tender synovial fold or "plica" may be palpated in this region around the patella. Examination should proceed with palpation of the tibial tuberosity followed by the patellar tendon and the inferior pole of the patella; the site of tenderness in patellar tendonitis.

Examination of the patella should then be undertaken. The superficial surface is easy whilst the posterior surface may be palpated by displacing the patella to the medial side and palpating the exposed undersurface and repeating the manoeuvre to the lateral side. The patella should then be compressed against the femur as it is gently moved to the medial and lateral side and up and down. This manoeuvre may detect crepitus and roughness within the patello-femoral joint, pain may also be elicited. The patello-femoral joint should also be compressed as the knee is flexed. This may elicit crepitus and this test may also reproduce the pain experienced.

If patello-femoral subluxation or dislocation is suspected, the apprehension test is performed in which the patella is displaced laterally whilst the knee is extended. Apprehension may be produced by the fear of an impending dislocation and the knee is involuntarily flexed to prevent the patella subluxing. This test is usually negative if dislocation has not previously occurred. If the excursion of the patella to the lateral side is restricted by a tight lateral patellar retinaculum, lateral patella hyperpressure syndrome may be suspected in which the tight lateral retinaculum tilts the patella laterally during flexion compressing the lateral side of the patello-femoral joint causing pain.

6 Radiography of the Patello-Femoral Joint

The plain antero-posterior and lateral films are not ideal for pathology suspected of being in the patello-femoral joint. Although the anterior-posterior view may demonstrate a bipartite patella in which the patella develops in two parts. The lateral view of the knee may demonstrate patella osteophytes although this is usually only at a fairly advanced stage of arthritis. The lateral view may show a patella alta (high patella) which is associated with patella subluxation and dislocation, or a patella baja (low patella) associated with retro patella pain and arthritis. Osgood-Schlatters disease in which partial separation of the tibial tuberosity apophysis, or Sinding Larsen Johansen's disease at the inferior pole of the patella, may also be identified.

The best radiograph for the demonstration of patello-femoral pathology is the skyline view taken in 30 degrees of knee flexion. This demonstrates subluxation, patella tilt, lateral patella hyperpressure and any arthritis or thinning of the articular cartilage. Further information may be obtained by repeating the skyline radiograph at 60 and 90 degrees of knee flexion. The concept of patello-femoral tilt was described by Lauren. He described the lateral patello-femoral angle as a measurement often used in the interpretation of radiographs. In the presence of patello-femoral tilt, this angle may be reduced as the patella tilts to the lateral side. It is important not to be confused as patello-femoral tilt may or may not exist with radiological subluxation in which the patella is displaced laterally.

Arthoraphy is not now commonly used as scanning techniques reveal much more information. However arthoraphy does demonstrate synovial folds or plicae within the joint which are not well demonstrated by MRI scanning.

Computerised Axial Scanning (CAT) of the patello-femoral joint has been superseded by Magnetic Resonance Imaging (MRI). MRI is the imaging technique which reveals most information in patello-femoral pathology. The relationship of the patella to the femoral trochlear is well shown. Any synovial folds or plicae in the patella retinaculum or fibrosis of the fat pad may be seen. Occasionally intra-articular tumours are demonstrated. Using sagittal or coronal sections, defects in the articular cartilage can be shown on the patella or femoral trochlear. Other conditions, particularly those associated with soft tissue inflammation such as patellar tendonitis, are clearly defined.

Radio-isotope scanning of the knee is sometimes useful in demonstrating those parts of the knee which have an increased bone metabolism. In this way active and possibly symptomatic areas may be demonstrated.

Reflex sympathetic dystrophy may affect the patella after a minor injury or surgery. This condition is difficult to diagnose but may result in chronic knee pain and stiffness of the knee. A radio-isotope bone scan demonstrates a characteristic increased uptake in the affected area.

7 Classification of Anterior Knee Pain

Patello-femoral disorders causing anterior knee pain were well classified by Merchant in 1988. The classification divides the causes of anterior knee pain into acute trauma, repetitive trauma, the late effects of trauma, patello-femoral dysplasia, idiopathic chondromalacia, osteochondritis dissecans, synovial plica and patello-femoral arthritis.

8 Patello-Femoral Dysplasia

The most difficult area of classification is dysplasia of the patello-femoral joint. Patello-femoral maltracking is a clinical sign which is exceedingly difficult to describe, quantify or classify. It is best seen while the knee is flexed while the examiner stands above the knee and looks down along the patello-femoral joint. In a normal situation the patella follows a straight course as the knee flexes. The patella moves down in to the femoral trochlear groove and into the intercondylar region. In lateral maltracking the patella may move laterally particularly in the first 20 to 30 degrees of knee flexion before then moving medially to enter the patello-femoral groove. The patella may or may not again move laterally beyond 70 degrees of knee flexion. This may be associated with an increased tibio-femoral 'Q' angle and external tibial torsion. Lateral patella tracking is associated with anterior knee pain and chondromalacia although the relationship has not been clearly identified.

9 Lateral Patellar Hyperpressure

As described this condition in which excessive tightness in the lateral retinaculum produces lateral tilt and excessive compression in the lateral facet of the patello-femoral joint. The sky line radiograph, taken at 30 degrees of knee flexion, may show lateral tilt of the patella onto the lateral facet. This condition is associated with, and possibly produces, chondromalacia patella on the lateral patella facet and eventually produces lateral facet osteoarthritis of the patello-femoral joint. This is one of the conditions in which lateral release of the patella may have good results and possibly prevent the progression to arthritis of the patello-femoral joint.

10 Patello-Femoral Subluxation

Patello-femoral subluxation may be obvious when the patient recounts episodes in which the patella partially dislocates prior to relocating in the patello-femoral joint. Alternatively, the knee may have a feeling of being weak or giving way particularly whilst descending stairs or during sporting activities. Clinical examination may reveal lateral subluxation or lateral patello-femoral tracking. Additional signs such as patella alta, hypoplastic lateral femoral condyle, increased femoral-tibial 'Q' angle, persistent femoral anteversion, external tibial torsion or multiple ligamentous laxity may be present. Clinical examination may reveal a positive apprehension test. Sky line radiographs taken at 30 degrees of knee flexion may demonstrate patello-femoral tilt or overhang. The sky line radiograph may demonstrate overhang of the lateral border of the patella beyond the lateral femoral condyles. The patello-femoral congruence angle as described by Merchant may be beyond the normal 16 degrees. CT or MRI scans have recently been demonstrated to be very effective in the demonstration of patello-femoral subluxation. Scanning has the advantage in that it can be performed with the knee in full extension or 10, 20 and 30 degrees of knee flexion when minor degrees of patello-femoral subluxation may be demonstrated, whereas these minor degrees of subluxation may not be apparent on the sky line view taken at 30 degrees of knee flexion.

Patello-femoral subluxation or dislocation may be associated with damage to the medial facet of the patella or even chondral or osteochondral fractures.

11 Chondromalacia PatellaeChondromalacia

Like anterior knee pain, Chondromalacia is not a syndrome. Chondromalacia is the pathological appearance of fragmentation of the articular surface of the patella. The condition is usually associated with knee pain and chondromalacia has been reported as being present in 60% of normal adolescent children. One must also remember that the articular cartilage is insensitive. If the articular cartilage fails to distribute the load, excessive force is then transmitted to the subchondral bone plate, deformation of the bone occurs which is interpreted by the feeling of pain. It must be remembered that the fronds of cartilage seen are not the cause of pain but are produced by excessive stress. Removal of any functional articular cartilage whilst removing loose fronds of articular cartilage is detrimental as additional stress will be borne by the subchondral bone plate producing more not less pain.

If the chondromalacia is of Grade 3 or 4, in which full thickness damage has occurred to the articular cartilage, then debridement of the loose articular cartilage may reveal the subchondral plate. In such circumstances, abrasion chondroplasty or drilling of the subchondral bone plate may be undertaken in an attempt to allow the ingress of fibrous tissue to cover the exposed bone. However, as one might expect, the fibrous tissue which covers the defect will only partially replace the function of the articular cartilage. The resistance of the fibrous scar to abrasion will be limited.

Chondromalacia may be secondary to lateral hyperpressure or patello-femoral subluxation when it is limited to the lateral facet. Medial facet chondromalacia may be associated with episodes of patello-femoral dislocation. In this way, chondromalacia may be secondary to other pathological conditions and treatment of the primary cause may alleviate the problem. Idiopathic chondromalacia also exists in which the patella may generally be affected. In idiopathic or generalised chondromalacia the treatment is much more difficult. A reduction in patello-femoral contact force may be produced by a Maquet type osteotomy advancing the tibial tuberosity forwards. This reduces the patello-femoral contact force but may be associated with a reduction in patello-femoral contact area and therefore not relieve the patello-femoral pain. At best improvement is only in 50% of patients, whilst the deformity and scar is commonly disfiguring.

Chronic patello-femoral dislocation may be congenital or acquired. The acquired condition is usually associated with intra muscular injections into the quadriceps muscle during the neonatal period. A progressive fibrosis of the quadriceps muscle occurs which eventually produces recurrent, then habitual and finally chronic patello-femoral dislocation.

12 Osteochondritis Dissecans

Osteochondritis dissecans was first described by Andrew Parry who removed a loose body in 1558. Paget described quiet necrosis of the knee in 1870 although Conning first described osteochondritis in 1888. Osteochondritis may present as anterior knee pain, recurrent swelling, locking or giving way. The most common site is on the lateral aspect of the intercondylar region of the medial femoral condyle. The lateral femoral condyle or patella may also be affected. The arthroscopic treatment of osteochondritis was reviewed by Gull in 1985. Arthroscopic fixation of a loose osteochondral fragment of the patella may require knee arthrotomy. If the fragment of bone has become detached or fragmented and replacement with fixation is inappropriate, debridement of the defect may be undertaken arthroscopically.

13 Synovial Plicae

Recently the important of synovial plicae in the production of anterior knee pain has been recognised (Johnson et al 1984). Plicae may cuase pseudolocking and may even mimic acute internal derangement of the knee (Hughston et al 1963, Pipkin 1971). The presentation of the syndrome may be delayed until symptoms are precipitated by inflammation within the plica secondary to an injury or a diminution in the elasticity of the plica which occurs with age. The symptoms are due to the plica bowstringing, across, or clicking over the femoral condyle on knee flexion (Patel 1986).

Plicae represent the remnants of the three separate synovial cavities present in the synovial mesenchyme of the developing knee which coalesce into one cavity at the 12 week stage of foetal growth (Gray and Gardner 1950). If the reabsorption of the divisions between the superior, the medial and the lateral cavities is incomplete then a medial supra-patellar plica, a lateral supra-patellar plica, or alternatively, a supra-patellar membrane may result depending on the degree of reabsorption . A supra-patellar membrane may be complete such that a separate supra-patellar pouch exists which does not communicate with the knee joint. The membrane may be incomplete with an opening or 'porta' from the supra-patellar pouch into the knee joint proper. Incomplete reabsorption elsewhere in the knee may result in the medial or lateral shelf or the anterior plica (Ogata and Uhthoff 1990).

Synovial plicae of the knee were first described in anatomic dissections by Fullerton in 1916, and by Mayeda in 1918 (Fullerton 1916, Mayeda 1918). The plicae were variously named ligamentum alaria, plica alaria, ligamentum mucosa, medio-patellar plica or a lateral alar fold. The arthroscopic appearances were first described by Lino, in 1939, and subsequently by Patel and Watanabe. He classified their appearances into four types (Lino 1939, Patel 1978, Watanable, Takeda and Ikeuchi 1979). The medial and lateral bands along the upper border of the patella in a horizontal plane are the supero-medial plica or supero-lateral plica, or a supra patellar membrane. The plicae to the medial and lateral side of the patella running from the fat pad to the side of the patellar retinaculum in the coronal plane are the medial or lateral synovial shelf . The fold running from the fat pad to the intercondylar notch of the femur overlying the anterior cruciate ligament is called the anterior plica and is the most common plica in the knee. The medial shelf is the next most frequently encountered plica, the lateral shelf being less common. A complete supra-patellar membrane has been reported to be present in 2% of knees, incomplete membranes being more common (Johnson 1981). The plica syndrome has been reported in siblings (Reid et al 1980).

Post-mortem studies have shown plicae to occur in 20 - 50% of normal people (Hardaker, Whipple and Basset 1980, Wilhelm 1983, Zanoli and Piazzai 1983), with the highest incidence of people of Japanese descent (Mayeda 1918, Lino 1939, Aoki 1965, Sakakibara 1976, Jackson, Marshall and Fujisawa 1982). A 40 - 80% incidence of synovial plicae in arthroscopic examinations has been reported (Mizumachi, Kawaiashima and Okamura 1948, Broukhim et al 1979, San Dretto et al 1982, Johnson 1981, Dandy 1986).

There is some controversy as to the prevalence of the plica syndrome and some reports even suggest that the pathological synovial plica does not exist, the plicae being a normal vestigial finding present in up to 60% of normal knees (Jackson 1980, Dandy 1981, Dandy 1986). Jackson, Dandy and others believe that plicae may be pathological but that over-diagnosis of the syndrome occurs, and many normal synovial shelves are removed (Jackson 1980, Hardaker, Whipple and Basssett 1980, Jackson, Marshall and Fujisawa 1982, Apple 1983, Zanoli and Piazzai 1983, Dupont 1985, Broom and Fulkerson 1986, Dandy 1986, Patel 1986, Lupi et al 1990). Dandy considered only 1% of synovial plicae to be associated with a symptomatic medial shelf syndrome, and that the other plicae are not pathological (Dandy 1986). Conversely other authors consider the plica syndrome to be a common cause of anterior knee pain and often mis-diagnosed. It has been claimed that the supra-patellar membrane is virtually never asymptomatic (Nottage et al 1983, Fujisawa, Jackson and Marshall 1976, Johnson 1981).

Attempts have been made to quantify the occurrence of pathological plicae by analysing the histological findings of arthroscopic plical biopsies. Wilhelm reported histological findings of fibrosis indicative of chronic inflammation in 15% of a series of 186 medial shelf biopsies (Wilhelm 1983). Whilst Mital rpeorted plical haemorrhage in 9 of 16 biopsies (Mital and Hayden 1979).

Sherman described a set of criteria for the diagnosis of pathological synovial plicae. The criteria consisted of: 1) a history of the appropriate clinical symptoms, 2) the failure of conservative treatment, 3) the arthroscopic findings of a plica with an avascular fibrotic edge which impinged on the medial femoral condyle during knee flexion, 4) no other knee pathology which would explain the symptoms (Sherman and Jackson 1989). However Jackson commented that the severity of symptoms is not proportional to the size or breadth of the synovial plica (Jackson, Marshall and Fujisawa 1982), and Richmond found no correlation between the duration of symptoms and the presence of pathological changes in the plica (Richmond and McGinty 1983). It has been suggested that an impingement lesion, which is a localised area of chondromalacia at the site of femoral condyle impingement is evidence that a plica is pathological.

Detection of synovial plicae as the cause of anterior knee pain is dependent on recognition of the relevant clinical symptoms and the absence of signs except perhaps for a palpable tender synovial band. Plicae are not well seen on plain radiographs, but a double contrast arthrogram may demonstrate the supra-patellar membrane and a synovial shelf. Double contrast arthrography may demonstrate a supra-patellar plica in 20% of cases (Pipkin 1950, Apple et al 1982, San Dretto et al 1982, Aprin, Shapiro and Gershwind 1984, Lupi et al 1990). The arthrographic appearances of the anterior plicae are often mistaken for the anterior cruciate ligament (Brody et al 1983). A synovial shelf is more difficult to demonstrate by arthrography but the sky line view may demonstrate the synovial shelf (Deutsch et al 1981, De la Caffiniere, Thijn and Hillen 1984).

Ultrasonography has been reported as having a sensitivity of 92% and a specificity of 73% in the detection of plicae (Derks, de Hooge and Van Linge 1986). A radio-isotope technetium bone scan may show some local increased uptake in association with an impingement lesion on the femoral condyle, but is otherwise normal (Brill 1984, Dye and Bell 1986). Computerised axial tomography (CT) has proven useful in the visualisation of the supra-patellar membrane but the synovial shelf or plica is easily missed (Boven, De Boeck and Potvliege 1983, Schutzer, Ramsey and Fulkerson 1986). The axial images of a Magnetic Resonance Scan (MRI) has in one study, proven to be a more useful mode of investigation than a CT scan for the detection of synovial plicae and chondromalacia (Passariello et al 1986). Radiographic and other modalities of investigation may be helpful in the clinical situation where the diagnosis is in doubt but are not routinely used in the detection of the plica syndrome which remains a clinical diagnosis confirmed during arthroscopy.

The results of the treatment of anterior knee pain are notoriously difficult to assess objectively, primarily because a wide variety of conditions are usually gathered together under the category of anterior knee pain or chondromalacia patella (De Haven, Dolon and Mager 1979). In addition little account is taken of the reported natural improvement in the symptoms of anterior knee pain with time (Goodfellow, Hungerford and Woods 1976). Studies in this field must analyse the conditions included carefully and a randomised control group with long term assessment is necessary (Bentley and David 1984).

The conservative treatment of the plica syndrome involves; quadriceps, hamstring and gastrocnemious stretching and isometric strengthening, cryotherapy, ultrasound, microwave diathermy, patellar bracing, bicycle riding, anti-inflammatory medication and an altered sports training schedule (Zanoli and Piazzai 1983, Newell and Bramwell 1984, Fisher 1986, Subotnick and Sisney 1986, Amatuzzi, Fazzi and Varella 1990). The results of such treatments in an uncontrolled study were an improvement in 40% of cases over a one year period (Rovere and Nichols 1985). Conversely Aprin suggested that, in knees in which an arthrogram demonstrated impingement of the plica on the femoral condyle in flexion, conservative treatment resulted in no long term improvement (Aprin, Shapiro and Gershwind 1984).

Injection of the synovial plicae with steroid and local anaesthetic in another uncontrolled study gave excellent results in 73% of patients (Rovere and Adair 1985), although percutaneous injection of the thin intra-articular band of the plicae must be difficult and reliable placement impossible.

Unfortunately all the historical studies on the surgical treatment of the plica syndrome are uncontrolled, non-randomised and often include a variety of pathologies (Patel 1978). Open knee arthrotomy and excision of the plica was first reported by Hughston (Hughston, Andrews and Waddell 1973) but has subsequently been reported by other authors (Patel 1978, De la Caffiniere, Mignot and Bruch 1981, Moller 1981). Arthrotomy has been superseded by the arthroscopic treatment of plicae which has been associated with good results in 60 - 90% of cases (Mital and Hayden 1979, Watanabe, Takeda and Ikeuchi 1979, Jackson, Marshall and Fujisawa 1982, Vaughan-Lane and Dandy 1982, Richmond and McGinty 1983, Zanoli and Piazzai 1983, Kinnard and Levesque 1984, Bough and Regan 1985, Koshino and Okamoto 1985, Broom and Fulkerson 1986, O'Dwyer and Peace 1988, Sherman and Jackson 1989). Arthroscopic plical excision has also been demonstrated to reduce the magnitude of the knee audiogram (Johnson 1981).

Chondromalacia patellae is commonly found in association with synovial plicae (O'Dwyer and Peace 1988). This is thought to be an association of two separate conditions in the same population (Patel 1978, Hansen and Boe 1989). Some studies have demonstrated inferior results following arthroscopic plica surgery when other pathologies such as chondromalacia patellae or patello-femoral subluxation are simultaneously present in the knee (De la Caffiniere, Mignot and Bruch 1981, Vaughan-Lane and Dandy 1982, Richmond and McGinty 1988, O'Dwyer and Peace 1988, Sherman and Jackson 1989). The overlap between the plica syndrome, lateral retinacular pain and lateral facet hyperpressure syndrome is indistinct (Larson et al 1978, Schulitz, Hille and Kochs 1983) and the conditions may co-exist. The situation following surgery may be further confused by a lateral release performed for lateral retinacular pain or the lateral hyperpressure syndrome which may also divide any plicae present (Merchant and Mercer 1974, Larson et al 1978, McGinty and McCarthy 1981).

The main complication reported following arthroscopic surgery for synovial plicae is recurrence of symptoms in 5% of cases (Richmond and McGinty 1983, Johnson et al 1984). This may result from reformation of the synovial band following simple incision of the plicae, or scar formation around the base of the excised plicae (Dandy 1981, Johnson et al 1984, Anderson and Poulson 1986). A case of lateral patella subluxation has been reported following over-zealous resection of a medial shelf and the medial retinacular structures (Limbird 1988).

As yet the only scientific study which shows synovial plicae to be pathological or that division of the plicae is of any benefit to the patient as compared to the natural improvement in adolescent anterior knee pain which occurs with the passage of time is that reportedly the author (Johnson et al 1984). This study was able to determine that the synovial plicae of the knee are indeed a pathological entity rather than a normal variant, and was able to determine that arthroscopic division had a short and long term patient benefit when compared to a randomised control group.

14 Patello-Femoral Arthritis

Patello-femoral arthritis may be secondary to trauma, lateral hyperpressure, lateral patello-femoral subluxation, patello-femoral dislocation or osteochondritis dissecans of the patella. Posterior cruciate instability produces excessive load in the patello-femoral joint and may be associated with early degenerative change. Fixed flexion deformity of the knee or hip may also cause premature changes in the patello-femoral joint due to excessive patello-femoral contact force.

Primary osteoarthritis of the patello-femoral joint may be particularly prevalent in pyrophosphate crystal arthropathy, pseudo gout or the hypertrophic variety of osteoarthritis. In both these conditions the patello-femoral joint may be affected by a florid and advanced arthritis whilst the tibio-femoral joint is well preserved.

15 The Conservative Treatment of Anterior Knee Pain

The conservative treatment of anterior knee pain must initially consider the extraneous causes. The running or playing surface may need changing at least temporarily such that jogging or running can be performed on grass or a soft surface rather than pavements or concrete. The shoe wear may be changed with specialised shoes used for activities such as road running. Additional custom made orthoses may be necessary to correct excessive foot pronation, metatarsalgia, hallux rigidus, calcaneal varus or valgus, equinus, femoral anteversion or external tibial torsion.

Physiotherapy should be directed towards flexibility, posture, muscular strengthening and the alleviation of inflammation. Objective isokinetic muscular assessment may be undertaken using a Kin-Com, Cybex or other similar computerised dynamometer. In these machines the muscle strength is tested throughout the range of motion and a graphic record of muscle function is produced. This graphic record may be compared to the results from the opposite side or with the results from the same side at different times during the rehabilitation. The muscular balance between the quadriceps and hamstrings muscles and between the concentric and eccentric modes of muscular contraction may be compared and rehabilitation specifically concentrated on the observed areas of weakness.

In the discussion of this modality it is important to understand the terms used. Isometric exercises are undertaken with the maintenance of muscular contraction at a constant low length with variable loads. Isotonic activity is undertaken using muscular contraction against a constant load varying the speed and the length of the muscles. Isokinetic activity is undertaken with muscular contraction at a constant angular velocity. The load and length of the muscle are varied. Concentric muscular contraction is undertaken where shortening of the muscle length occurs against loads. Eccentric contraction is where the muscle lengthens against a load. A recent study demonstrates that the eccentric mode of isokinetic activity may be the most sensitive in diagnostic evaluation and also in muscular retraining.

When using isokinetic measurement in the assessment of the various patterns of activity, the phased hamstring eccentric isokinetic analysis undertaken with an angular velocity of 180 degrees per second. A deficit in function is revealed particularly associated with loose bodies, torn lateral meniscus and osteochondral defects. Whereas synovial plicae characteristically cause a reduction in the peak torque generated between 40 and 80 degrees of flexion during eccentric quadriceps activity at 60 degrees per second, the investigation may also be used to assess the results of surgery in that the pattern of activity may be restored to normal after excision of a synovial plica or other pathology.

The continual assessment is also useful during a rehabilitation phase to analyse the return of muscular strength and to determine when return to full activity is possible. This has been extensively used in association with the rehabilitation of anterior cruciate surgery whereby return to full sporting activities is usually allowed only after the attainment of 90% of the muscular strength of the normal side.

Other mechanical and electrical modalities of physiotherapy such as cryotherapy, ultrasound and mega-pulse electro-therapy may be used when soft tissue inflammation is present. Patello-femoral bracing or taping to stabilise the patello-femoral joint or to correct lateral maltracking may relieve the pain from lateral patella tracking or patella subluxation. McConnell, an Australian physiotherapist, described a complete programme of patello-femoral rehabilitation which included retraining and strengthening the vastus medialis muscle using bio-feedback to promote vastus medialis action early in the phase of knee flexion.

Such conservative therapy may be supplemented by non steroidal anti inflammatory medication as necessary, a steroid injection into extra-articular soft tissues and non weight bearing tendons may be of benefit. Injection into weight bearing tendons such as the Achilles tendon should be discouraged as rupture may be precipitated. Repeated intra-articular injections have been reported to result in damage to the articular cartilage and should be avoided. Temporary periods of rest may also alleviate the symptoms.

There are studies which suggest that conservative treatment in anterior knee pain may result in an initial improvement in up to 87% of patients. However this diminishes to 60% on follow up at 3 months. A study by Goodfellow et al demonstrated that, in a cohort of female patients with anterior knee pain, 49% of patients improved following an average 16 month duration of conservative therapy (Goodfellow et al). However it was also noted that 96% of patients retain some anterior knee pain at final follow up.

In a recent study undertaken by the author in patients with synovial plica syndrome, improvement occurred in only 28% of patients over a 2 year period treated by diagnostic arthroscopy and conservative measures (Johnson et al 1984). This compares with a 96% improvement following surgical division of the synovial plica. Thus the expected improvement in the symptoms of anterior knee pain with time may be sustained by hope and frustration rather than any objective evidence.

16 The Surgical Treatment of Anterior Knee Pain

The surgical treatment of anterior knee pain may include excision of the degenerative area within the patellar tendon in patellar tendonitis. The central portion of the patellar tendon may be released from the inferior pole of the patella although this may be unnecessary and may reduce the strength of the patellar tendon. Peri-patellar bursitis may be treated by aspiration, injection or excision if necessary. Arthroscopic surgery may be undertaken to remove anterior meniscal tears, remove meniscal cysts, decompress meniscal cysts, remove loose bodies in the front of the knee and debride areas of osteochondritis dissecans.

Cruciate ligament reconstruction may alleviate the anterior knee pain associated with anterior or posterior cruciate ligament laxity. However, any retro-patellar articular degeneration may not be reversible. Following anterior cruciate ligament reconstruction using either the central third of the patellar tendon or a hamstring tendon reconstruction technique, an instance of post operative anterior knee pain has been noted. Attention to detail during surgery may reduce this incidence. Arthroscopy and arthroscopic excision of the fat pad may be undertaken in Hoffa's syndrome where the hypertrophic fat pad or infra-patellar xanthoma may be removed. The condition of peri-patella pannus formation or quadriceps fibrosis where an excessive fibrous reaction occurs in the synovium around the patella. The hypertrophic synovium encroaches into the patello-femoral joint causing impingement and pain. Local synovectomy may be of benefit. In similar way, synovial tumours such as lipoma, pedunculated fibromas, intra-articular xanthomas and areas of pigmented villo-nodular synovitis may be arthroscopically excised. It may also be possible to remove benign bony tumours around the knee such as solitary enchondroma arthroscopically.

In the condition of lateral patellar hyperpressure syndrome, lateral patellar tilt and lateral patello-femoral facet chondromalacia, lateral retinacular pain, lateral retinacular nerve injury or patello-femoral subluxation, arthroscopic lateral retinacular release may give symptomatic relief.

17 Patello-Femoral Subluxation

Minor degrees of patello-femoral subluxation without dislocation, may be relieved by arthroscopic lateral release although there is a described incidence of recurrence. Risk factors include multiple ligamentous laxity, patella alta, hyperplastic femoral condyle, increased 'Q'angle, external tibial torsion, persistent femoral anteversion or an avulsed and ruptured vastus medialis. In athletes having sustained a single dislocation of the patello-femoral joint, However it is generally advised that undertaking early knee arthroscopy, drainage of the haematoma, debridement of any articular damage and arthroscopic lateral release followed by early rehabilitation including quadriceps strengthening exercises is good practice. Empirical lateral release for anterior knee pain is undertaken in some centres but must be strongly discouraged, as inappropriate lateral release may produce medial patella dislocation and other problems.

In patients with recurrent patello-femoral subluxation, as an initial procedure use arthroscopic lateral release in isolation unless multiple ligamentous laxity or other gross deformity is present. In the presence of risk factors or multiple ligamentous laxity, I prefer to combine arthroscopic lateral release with repair of the vastus medialis and transposition of the vastus medialis to the anterior medial surface of the patella. Combine this with an extra-articular modified Elmsley-Trillat procedure in which the tibial tuberosity is elevated on a distal base, rotated medially and fixed with a single screw. In many instances, if fixation is adequate, early rehabilitation can be undertaken without the need for an immobilisation in a plaster cast or splint. Discharge from hospital may take place after 1 or 2 nights and early return to full activity after only 6 weeks may be expected. This procedure leaves only two 2 cm long scars at the superior medial border of the patella and to the lateral side of the tibial tuberosity. There is minimal inhibition of the quadriceps muscle and no ugly deformity or scarring of the knee results.

18 Chondromalacia

Arthroscopic surgery for chondromalacia or articular cartilage defects in the patello-femoral joint is difficult and the results of such treatment are not well defined. Generally loose articular fronds and fragments may be removed. Any articular cartilage adherent to the subchondral bone may be assumed to be functional and should not be removed only to improve the visual appearances. Abrasion chondroplasty or articular drilling with a 1 mm drill are the techniques for abrading the exposed subchondral bone in the base of articular defects in order to promote the ingress of fibrous tissue. This tissue may cover the exposed bone and provide a new articular surface composed of fibrous scar tissue. This may in some cases relieve for a time the pain experienced. The fibrous tissue is never as good as articular cartilage and therefore excision of the loose articular fragments and fronds should be kept to a minimum. It is suggested in the literature that the maximum area of exposed bone which may be helped by an abrasion chondroplasty may be as small as 1 cm in diameter.

Chondromalacia of the femoral trochlear groove presents a difficult problem. This situation is commonly found in association with netball, basketball and Australian Rules football which require jumping. Abrasion chondroplasty is usually undertaken.

Arthroscopic surgery for chondromalacia in other sites should also be directed to the primary cause if one is present. If the chondromalacia is secondary to lateral hyper-pressure, lateral patello-femoral subluxation or dislocation, then this is treated while the chondromalacia is merely debrided. In the presence of chondromalacia of the central ridge or more generalised over the whole patella there is usually no definable cause treatable by arthroscopy, and this may be resistant to all other measures. In this situation subsequently a Macquet type advancement of the tibial tuberosity may be undertaken in mature patients. This should only be undertaken after due consideration in view of the ugly scar, the resulting deformity of the knee and the expected success in only 50% of patients.

19 Patellectomy

Surgical removal of the patella or patellectomy should be avoided if at all possible despite persistent anterior knee pain. There is persistent weakness of the quadriceps muscle which has been estimated to be as much as 30% which results in poor function, and in addition, excessive compressive forces are transmitted to the tibio-femoral joint and acceleration of any degenerative change in the knee joint occurs. Although total knee replacement in the absence of a patella is technically possible the resulting function is poor. Patellectomy is associated with persistent knee pain, the formation of bone fragments beneath the patellar tendon which may cause persistent anterior knee pain. Late debridement and lateral release of the repaired quadriceps/patellar tendon may be necessary because of persistent anterior knee pain, lateral retinacular pain, lateral tendon subluxation and restricted knee flexion.

20 Effectiveness of Treatment for Anterior Knee Pain

Conservative management for anterior knee pain is sufficient and adequate for approximately 50% of patients, of those remaining a clinically definable pathology is present in perhaps 80% to 90% of patients. Of these patients, a significant proportion may be amenable to surgical therapy. There does, however, remain a proportion of patients complaining of anterior knee pain in which no definable pathological cause or effective treatment may be found. In these cases, reflex sympathetic dystrophy must be considered in a small proportion, although the treatment of reflex sympathetic dystrophy is difficult.

21 Conclusion

The management of anterior knee pain demands an understanding of the numerous pathological entities which may cause it. A careful relevant history and examination is necessary. If properly organised conservative treatment is unsuccessful a variety of surgical procedures are available. Successful treatment may be possible in up to 90% of patients, whereas without proper treatment there is little evidence that the symptoms will settle without treatment. Adequate treatment my be successful in a significant proportion of cases and in some conditions such as lateral patella tilt and hyper-pressure, the progression to patello-femoral arthritis may be avoidable. The attitude held by some practitioners that anterior knee pain is a self limiting condition in patients with underlying neurotic personalities should be discounted, discarded and condemned to the historical archives of orthopaedic surgery.

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