R.T. Strother, MD, CCFP D. Samoil, MD Patellofemoral Syndrome: Therapeutic Regimen Based on Biomechanics SUMMARY RESUME The clinician needs to rehabilitate the Le clinicien doit baser son traitement du syndrome patient with the patellofemoral syndrome femoro-rotulien sur des notions de biomecanique et d'anatomie. Si nous comprenons la physiologie de la based on biomechanics and anatomy. If we rotule et les forces qui lui sont imposees, nous understand the function of the patella and sommes capables d'eduquer nos patients afin de the forces acting upon it, we can educate maximiser l'observance tout au long du traitement et our patients to ensure their compliance le maintien de bonnes habitudes ulterieurement. through both the treatment phase and future maintenance. (Can Fam Physician 1989; 35:1649-1654.) Key words: patellofemoral syndrome, sports medicine Dr. Strother is Assistant Professor understanding of patellofemoral dis- years is significantly above the mean of Family Medicine and Chairman of ease before initiating treatment. All (21.6) for all other athletic the Sports Medicine Committee, of these areas should be considered injuries.8'-2 Department of Family Medicine, when developing a practical thera- The frequency of injuries increases University of Calgary. Dr. Strother is peutic regimen. during adolescence, and then remains also physician to Team Canada consistently high throughout early Badminton, Luge, and Volleyball. Dr. Incidence adult life, falling off only after the pa- Samoil is a Family Medicine Resident Patellofemoral pain is common.'-' tient approaches the sixth decade.'2 at the University of Calgary. Requests It occurs most often in young people Patellofemoral syndrome is a fre- for reprints to: Dr. R. Strother, Holy and appears to be related to athletic quent diagnosis that is widely distrib- Cross Hospital Family Medicine activities.6'7 In runners, anterior knee uted through many age groups. Clinic, 2202-2 St. S.W., Calgary, pain accounts for up to 57% of knee Alta. T2S 1S5 problems, representing the most fre- Symptoms quent complaint of this group.38-" The classic manifestation of patel- PATELLOFEMORAL syndrome In his survey of athletic injuries, lofemoral pain is retropatellar pain is a common clinical entity. Exer- Dehaven and Lintner'2 found that the that is aggravated by ascending or de- cise is intimately related to both the knee is the most commonly injured scending grades and prolonged sta- treatment and the development of body part, with patellofemoral pain tionary knee flexion.7 Symptoms usu- patellofemoral pain syndrome. In syndrome accounting for 7.4% of all ally begin insidiously and may persist susceptible individuals, inappropriate injuries in men and 19.6% of all inju- for months, with little progression or exercise may precipitate its develop- ries in women. This translates into change in severity. The dull, aching ment and may delay resolution when 18.1% of knee injuries in men and retropatellar pain may be well local- the patient is already injured. 33.2% of knee injuries in women. Of ized and is commonly bilateral.7 Of- The dynamic interaction of activi- all age groups ranging from 12 to 60 ten pain is precipitated by activity3 or ty, individual skeletal alignment, years old, patellofemoral pain was an increase in training mileage and is muscular strength, and flexibility, the most frequent complaint in the aggravated by ascending and de- and their effects on injury require groups aged 13 to 15 years and 25 to scending grades. The discomfort usu- that the clinician develop a total 40 years. The average age of about 26 ally persists for a time after activity, CAN. FAM. PHYSICIAN Vol. 35: AUGUST 1989 1649 with some relief obtained through at the centre of dynamic and static men for the same angle of knee rest. Aching commonly returns after controlling forces because therapy is extension.4 It follows that activities sitting, for example, in cars, during based on the concept of balancing that increase knee flexion under load flights, and at movie theatres.7"3 these divergent forces.7'21 predispose the individual to develop Patients with patellofemoral pain Contact areas on the underside of symptomS.4.7'26'27'29,30 may also report a subjective sensa- the patella vary with its position in The rich blood supply of the knee tion of instability, or giving way. A the groove.'7 The concept of varying comes from the anastomosis of five muscular "release" of the quadriceps contact areas and force distribution is major arteries. The patella, femoral has been proposed as an explanation important because pressure distribu- condyle, and tibial condyle have a of this symptom.7 This feeling must tion has been theorized to be a prima- wealthy intra-osseous blood supply. be differentiated from other similar ry contributor to the development of The adjacent soft tissues are well sup- symptoms of intra-articular and me- pain. Many surgical techniques di- plied by the circumpatellar anastomo- niscal lesions. Anterior knee pain is a rected toward relieving patellofemo- sis, a multilayered structure that in- symptom common to many diseases ral pain concentrate on correcting cludes subcutaneous fascia, of the knee joint,1415 which can be theoretically abnormal contact retinaculum, capsule synovium, and categorized by region (Table 1).10,.6 pressures. 1,7,13,18,22-25 Recent studies subchondral bone.3' When taking the history of knee pain, have shown, however, that the patel- The nerve supply to the knee con- the physician should keep in mind the lofemoral contact pressures are re- sists of posterior afferent nerves (in- spectrum of disorders that can affect markably uniform in all knees, cluding the posterior articular nerve the knee and their clinical signifi- whether symptomatic or not.26 At the and the terminal branch of the obtu- cance. least, contact area pressures are of rator nerve), the anterior afferent debatable value in directing therapy. nerves (including branches of the Biomechanics Biomechanically, the patella's femoral nerve to the quadriceps mus- In order to elucidate the various function is far more complex than cles), the common perineal nerve, factors involved in patellofemoral simply increasing the lever arm dur- and the saphenous nerve.32 The deep pain, it is useful to review the anato- ing extension and acting like a fric- fibrous substance of ligaments or my and biomechanics of the patello- tionless pulley. The joint acts as a le- menisci are aneural; however, the femoral articulation. The patella ver mechanism with different forces presence of mechanoreceptors in the functions, first of all, to centralize in the patellar ligament and the qua- joint capsule is well documented.32'33 and guide the forces of the divergent driceps tendon. Moreover, the ratio The synovium and subchondral muscle groups of the quadriceps.7"7 between ligament force and tendon bone have pain fibres.7 Articular car- Secondly, the patella acts to increase force changes as a function of the the effective lever arm of the quadri- knee flexion-extension angle.'8 ceps, providing both flexor and ex- Therefore, the patellofemoral joint Table 1 tensor mechanical advantage.7 7"8 Fi- acts more like a balance beam than a Causes of Anterior Knee Pain nally, the patella provides a pulley.27 This important new concept Patella protective bony shield for both func- calls for a re-evaluation of the angles Patellofemoral pain syndrome tion and cosmesis.'7 of flexion considered most suitable Patellar tendonitis Significant forces act on the patella for rehabilitation during seated knee Fat pad syndrome as it tracks proximally to distally in extension. General synovitis association with increasing knee flex- An understanding of the forces en- Quadriceps tendonitis ion. As it is drawn into the trochlear countered by the patella at varying Subluxing, dislocating patella groove (its articulation with the fe- degrees of flexion is the key to devel- Osgood-Schiatter disease mur), the patella travels a course oping a treatment protocol. Tradi- Prepatellar bursitis forming a gentle "C," open to the tionally it was thought that the patel- Retropatellar tendonitis side. Stability in the first 200 of flex- lofemoral joint contact pressure Medial ion is provided by soft tissues with increased linearly through ever-in- Pes anserinus bursitis support dependent upon muscle creasing joint flexion. New biome- Roschel's bursitis tension. 17"19'20 The muscle tension chanical evidence suggests that force Stress fracture provided by the quadriceps mecha- transmission through the knee joint Lateral nism involves the pull of two diver- may be influenced in a non-linear Bursitis gent forces. The vastus medialis mus- way by the level of the static Popliteus tendonitis cle, located distally and medially, acts preload.21 1liotibial band syndrome to stabilize the patella medially. In any case, the force transmitted Excessive lateral pressure syndrome Counteracting the vastus medialus from patella to femur will increase as Intra-articular muscle, the pull of the vastus lateralis flexion increases. At 900 of flexion, Torn meniscus, meniscal lesions muscle couples with the iliotibial approximately four times the body Ligament tear band. In addition, the forces of the weight is transferred through the pa- Arthritis patellofemoral medial and lateral lig- tellofemoral joint, and at 1200 of flex- Lpose body aments help maintain proper tracking ion, this transfer increases to about Medial synovial plica syndrome of the patella throughout its motion eight times body weight. Women Reflex sympathetic dystrophy along the knee joint.3'7 The clinician have been found to develop higher Osteochondritis dissecans must understand that the patella lies degrees of compressive force than Source: See references 10 and 16. 1650 CAN. FAM. PHYSICIAN Vol. 35: AUGUST 1989 tilage itself has no pain-receptive has generated considerable contro- subpopulation of patients who exhibit nerve endings and presumably causes versy. The accepted measurements a reluctance to have the patella dis- pain indirectly when products of de- vary widely.