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Anterior Knee Pain
Anterior Knee Pain
MICHAEL H. BOURNE, M.D., WILLIAM A. HAZEL, Jr., M.D., Department of Orthopedics; STEVEN G. SCOTT, D.O., Department of Physical Medicine and Rehabilitation; FRANKLIN H. SIM, M.D., Department of Orthopedics Anterior knee pain is a common symptom, especially in adolescence, and often no specific cause is sought or identified. Physicians who treat patients with knee pain should understand the normal anatomic features and the biomechanics of the patellofemoral joint. We review this information and discuss important aspects of the physical examination and roentgenographic evaluation in patients with anterior knee pain. Once the clinical cause of anterior knee pain has been established, directed nonoperative treatment including physical therapy should be initiated. Surgical intervention is generally reserved for patients in whom nonoperative management is unsuccessful and identifiable abnormalities exist.
Anterior knee pain is a frequent source of impairment. 1 Although the cause of such pain often remains unknown and the condition may be selflimited, 2 a specific diagnosis should be sought and appropriate treatment initiated. 3 ANATOMY The patella is the largest sesamoid bone in the human skeleton, and its undersurface possesses the thickest articular cartilage. 4 Primary ossification of the patella normally begins at age 4 to 6 years. The patella has three primary functions: (1) it increases the lever arm of the quadriceps mechanism, (2) it protects the anterior aspect of the knee, and (3) it enhances the cosmesis of the lower extremity. Normal joint function necessitates stability and strength. Static stability of the patellofemoral joint is provided by bony congruence between the patella and the trochlea of the femur, which varies with the position of knee flexion.5
Address reprint requests to Dr. F. H. Sim, Department of Orthopedics, Mayo Clinic, Rochester, MN 55905. Mayo Clin Proc 63:482-491,1988
Several ligamentous structures contribute to static stability, and the extensor mechanism provides strength and dynamic stability. 6 The articular anatomy of the patella is straightforward. The medial and lateral facets are separated by a vertical ridge. 4 A smaller facet, known as the odd facet, exists medially and is delineated by a second vertical ridge. Wiberg7 has classified patellar shapes. Most commonly, the lateral facet is larger than the medial facet, and both are concave. The corresponding femoral trochlear groove is also variable in shape and configuration. It may be broad and shallow or more V-shaped. 8 Therefore, the patellofemoral joints are inherently more stable in some persons than in others. During motion, the patella glides 7 to 8 cm with respect to the femur.7 When the knee is extended, the patella is at its most proximal point, but it does not seat into the trochlea until approximately 20° of flexion, at which point its most distal aspect contacts the trochlea. With further flexion, the patella slides distally and the contact areas become more proximal on the patella. At full flexion, only the most medial and lateral aspects of the proximal patella contact the femur.9
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The quadriceps mechanism h a s been well described anatomically (Fig. I). 6 It inserts in a multilaminar fashion. Superficially, the rectus femoris inserts anteriorly on the patella. A middle layer consists of the vastus lateralis and vastus medialis. The medial portion of the distal vastus medialis, known as the vastus medialis obliquus, inserts into the upper medial pole of the patella at an angle of 55° to 70° from the vertical. 10 Recently, the distal portion of the vastus lateralis has been described as the vastus lateralis obliquus. 11 Because the quadriceps muscle is aligned anatomically with the shaft of the femur and not with the mechanical axis of the lower extremity, a dynamic lateral force is applied to the patella during extension of the knee. 12 The importance of the vastus medialis obliquus is that it provides the only dynamic medial stability for the patella. 10 The ligamentous structures of the patellofemoral joint are complex. The medial and lateral retinacula form from structures in the first and second layers of the knee joint. 13,14 It is probably simplest to think of them as winglike structures
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that connect the patella to the femur, the menisci, and the tibia both medially and laterally. Within these wings are areas of condensation that form the patellofemoral ligaments. This patellar retinaculum is particularly important laterally, where it also inserts into the hamstring musculature; 15 hence, tightened hamstrings can lead to patellofemoral symptoms. Finally, several bursae are present around the knee joint (Fig. 2).16 The bursae and the anterior fat pad may give rise to a variety of syndromes that mimic patellofemoral disease. It is important to examine the knee to identify these sources of pain. BIOMEOHANICS An understanding of the patellofemoral joint biomechanics is essential to understanding pathologic conditions of the knee. Reilly and Martens, 17 among others, have examined the patellofemoral contact forces under a variety of loading conditions. 5,18 When the knee is extended from 90° of flexion to the neutral position against 9 kg of constant resistance, the patellofemoral reaction
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Fig. 1. Diagram of quadriceps mechanism.
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Fig. 2. Sites of bursae around the knee.
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force is maximal at 90° and declines to 0 at full extension. Conversely, the quadriceps tendon force, which is minimal at full flexion, increases dramatically as full extension is attained. When a weight is hung from the foot and the knee is extended, the maximal patellofemoral forces are attained at approximately 36° of flexion; again, however, the quadriceps muscle force increases near full extension. During deep-knee-bending conditions, the patellofemoral force increases with flexion, as does the quadriceps force. The pertinent biomechanics can be summarized as follows: near full extensions, the patellofemoral force is 0; during stair climbing, it can increase to 3.3 times the body weight; and with deep knee bends, forces approaching 8 times the body weight can be attained. 17 When the knee is moved through a range of motion against resistance, maximal patellofemoral forces are found between 35° and 40° of flexion.5'17 A direct relationship exists between the patellofemoral contact pressure and the function of the patella as a lever arm for knee extension. 19 Near full extension, the patella rides close to the shaft and the center of rotation of the knee and therefore provides a minimal lever arm for extension. With flexion, the patella rides up and over the trochlea and displaces the patellar tendon away from the instant center of rotation. This movement provides an increased mechanical advantage to the quadriceps tendon but also increases proportionately the patellofemoral contact pressure. The work of Maquet 19 and others 2& has demonstrated that elevation of the tibial tubercle results in decreased quadriceps and patellofemoral contact forces. From a geometric perspective, as shown in Figure 3, elevation of the tubercle increases the angles between the quadriceps tendon and the patellar tendon. With application of the parallelogram rule, when a larger angle is subtended, the resultant posteriorly directed force is decreased. The clinical significance of this principle will be discussed subsequently in this article. ETIOLOGIC FACTORS Anterior knee pain may be attributed to several sources, 21 including the synovium, periarticular structures, and lastly bone. Because articular cartilage is aneural, it cannot be implicated as a primary source of patellofemoral pain.
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Fig. 3. Patellofemoral contact force (Fc) is reduced with elevation of patellar tendon insertion. Fp = force of patellar tendon; Fq = force of quadriceps tendon. (From Ferguson and associates. 20 By permission of The Journal of Bone and Joint Surgery, Inc.)
Jackson 2 has implicated both biochemical and biomechanical causes for anterior knee pain. The two may not be mutually exclusive.23 Biomechanical factors can produce fissures and erosion on the articular surface. The release of lysosomal enzymes from any cause stimulates an ensuing synovial inflammation and results in pain and degradation of articular cartilage. 24 Although it has not been proved, some investigators have suggested that debridement of damaged tissue may decrease the production of lysosomal enzymes. 25 Rheumatic disease should be included when synovial sources of pain are considered. Biomechanical causes of anterior knee pain can be acute or chronic events. Acute events include dislocation of the patella, 26,27 patellar fracture, or bursitis. Chronic sources include recurrent patellar subluxation, 12,28,29 malalignment, 30 excessive lateral pressure syndrome, 31 meniscal injury, and traction epiphysitis, possibly accounting for Osgood-Schlatter disease, Larsen-Johansson disease, bipartite patella, 32 and proximal pole traction osteochondritis. 33
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Cartilaginous defects of the patella can be classified by location, occurring on the lateral, medial, or odd facet or as central defects along the median ridge. They can also be bipolar, involving both medial and lateral facets with a normal ridge, or they can be global. Lesions can be graded on the basis of distinguishing features on arthroscopic examination. Grade 1 lesions demonstrate softening and discoloration of the cartilage, grade 2 lesions show fibrillation and Assuring less than 1.3 cm in diameter, whereas grade 3 lesions show similar fibrillation involving an area not greater than 2.3 cm. Grade 4 lesions are evidenced by full-thickness cartilage loss with a mirror lesion on the femur.34 Cartilaginous lesions of the patella are ubiquitous and partially dependent on age. Wiles and associates 35 reported that they exist in only 26% of those younger than 20 years of age but in 75% of those between 20 and 29 years, 85% of those between 30 and 39 years, and in 100% of persons older than 50 years of age. In contrast, Heine 36 found an 80% rate of degeneration in the patella in the 50- to 59-year-old age group. More recently, Casscells 8 examined 300 knees in patients with a mean age of 70 years and found 58% with normal cartilage or grade 1 lesions of the patella. The presence of a lesion per se does not invariably correlate with symptoms. 37 In several studies, less than 50% of patients with lesions at arthrotomy were found to be symptomatic. 33 Furthermore, the development of changes on the patella seems to be clinically distinct from the onset of osteoarthritis. 9 Therefore, we believe that the term "chondromalacia" is vague, uncertain, and not useful as a diagnostic classification. It is a descriptive term that should be reserved for recording findings at the time of arthrotomy or arthroscopy. When cartilage has been damaged, its loadcarrying capacity is diminished and there is increased load transmission to the subchondral bone. This increased pressure might be the source of anterior knee pain. In 1980, Björkström and colleagues 38 found elevated intramedullary patellar pressures in patients with anterior knee pain in comparison with control subjects. The mean pressure of those with anterior knee pain was 44 mm Hg in comparison with 19 mm Hg in the control knees. Malalignment may cause a lateral compression syndrome that results in anterior knee pain. Sev-
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eral studies, however, have shown that a strong relationship between chondromalacia patellae and patella alta or between anterior knee pain and congruence and sulcus angles does not always exist. Traumatic injuries such as intraarticular fractures or osteochondritis dissecans are well-known causes of chronic knee pain. Other reasons for anterior knee pain are inflammation of various bursae, inflammation of the infrapatellar fat pad, avascular necrosis, synovial inflammation, impingement, 21 pseudochondromalacia patellae, 39 or plica syndrome. In some patients, no cause of anterior knee pain can be identified. In a follow-up study of a large group of adolescent girls with knee pain but no detectable abnormalities, Sandow and Goodfellow2 found that, at a mean of 4 years, most had persistent pain but few were restricted in activities or used analgesics. PHYSICAL EXAMINATION Physical examination of the patella is an integral part of the complete knee evaluation. The normal and the abnormal knee should always be compared and contrasted. A detailed history will complement and help direct the physical examination. Often patients will experience pain during prolonged sitting (positive theater sign), stair climbing, and knee-bending activities. Thorough examination of the knee is a complex task that should include evaluation of the foot, ankle, knee, and hip as well. We will discuss examination of the patellofemoral joint in detail. As an initial step, the varus or valgus alignment of the knee should be noted. A convenient measurement is the "Q" angle or that angle formed by a line between the center of the patella extending proximally to the anterosuperior iliac spine and extending distally to the center of the tibial tubercle (Fig. 4). Normally, this is less than 10° in men and 15° in women. 40 An excessive "Q" angle predisposes to lateral patellar subluxation or dislocation. The patient should be observed standing with the feet together and sitting with the knees flexed to 90° to determine the orientation of the patella with respect to the coronal plane. The patella may be internally rotated ("squinting") or externally rotated ("grasshopper eyes"), the position depending on femoral or tibial malrotation. Patellar motion should be observed while the patient is walking. Comparison of the quadriceps circumference at 10 cm proximal to
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Palpation of the patella may elicit crepitus or subluxation, which may or may not be painful. The patella is divided into longitudinal quadrants, and subluxation should be attempted both medially and laterally. Displacement of more than two quadrants (half of the patella) over the medial or lateral aspect is considered abnormal. Appreciable patient anxiety during attempted lateral subluxation is termed a "positive apprehension test" and is a sign of probable subluxation or past dislocation of the patella. Rarely, the patella can be completely dislocated at the time of examination. Excessive tilting of the medial or lateral aspect of the patella is evidence of laxity in the retinaculum.
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Fig. 4. The "Q" angle (or quadriceps angle), formed by extension of lines drawn from center of patella proximally to anterosuperior iliac spine and distally to tibial tubercle, denotes alignment of the knee. Excessive "Q" angle predisposes to lateral patellar subluxation or dislocation.
the medial joint line will often reflect subtle signs of quadriceps atrophy, particularly with respect to the vastus medialis obliquus. In patients with an acute patellar injury, this atrophy is usually not present. When the knee is fully extended and the quadriceps is relaxed, the patella should be fairly mobile. With flexion at 20°, the patella engages the trochlea, and structures on both the medial and lateral aspects of the knee begin to tighten. Tenderness or palpable defects in the retinaculum may be noted, and patella alta or baja may also be diagnosed with the knee in slight flexion.
RADIOGRAPHIC EXAMINATION In the past, radiographic examination of the patella and the patellofemoral joint has been hampered because standardized views have not been used. Familiarity with the variety of roentgenographic techniques used in evaluation of the patellofemoral joint is useful. On a plain anteroposterior film, the "Q" angle or quadriceps angle can be measured by using the angle formed by extending lines through the femoral shaft and the tibial tubercle to the center of the patella (Fig. 4). The "Q" angle can also be determined on clinical examination as the angle formed from lines drawn from the anterosuperior iliac spine to the center of the patella and from the center of the patella to the tibial tubercle with the knee in full extension. An increased "Q" angle suggests increased lateral pressure and possible subluxation. A lateral roentgenographic view is helpful in determining a second important criterion of patellar position—that is, its relative height, proximal or distal to the tibial tubercle. This characteristic has been termed, respectively, patella "alta" or patella "baja" and can be analyzed in several ways. Blumensaat 41 devised a test in which a lateral view roentgenogram obtained with the knee flexed to 30° is used. When the distal pole of the patella rides above the intercondylar condensation, patella alta exists. Perhaps more familiar and more accurate is the ratio described by Insall and co-workers,42 in which the height of the patella should be equal to the height of the patellar tendon (Fig. 5). This relationship is maintained for flexion from 20° to 70°. The
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knee flexion. Full flexion is used for a "sunrise" or "sunset" view, but the patella is well engaged in the trochlea at these points. Merchant and colleagues 44 began using 45° of flexion and devised the congruence angle (Fig. 6). The sulcus angle, which averages 138°, is that angle between tangents across the lateral and medial condyles (angle BAC in Figure 6). A line that bisects this sulcus angle (line OA in Figure 6) is used as a reference to a line drawn to the inferior portion of the patella (line DA). The angle formed (DAO in Figure 6) is termed the "congruence angle" and is normally -6° (being negative on the medial side and positive on the lateral side). An angle greater than 11° is outside the standard deviation and is considered to show lateral subluxation. A fourth measurement that is useful for determining patellar position was devised by Laurin and others. 43 With the knee flexed to 20°, the patella is just beginning to engage the trochlea and is at its position of maximal instability. The patellofemoral angle on the lateral aspect is then measured, as shown in Figure 7; if that angle is neutral (that is, the lines are parallel) or it opens medially, this finding is pathognomonic of lateral patellar tightness and subluxation. Thus, these four measurements—the "Q" angle, patella alta with use of the Insall ratio, the congruence and sulcus angles of Merchant, and the lateral patellofemoral angle of Laurin—in Fig. 5. The Insall ratio for determining relative patellar height. In normal knee, height of patella (P) should equal height of patellar tendon (PT).
length of the patellar tendon can slightly exceed the patellar height, but any ratio beyond 1.2 (tendon to patella) is considered abnormal and is suggestive of patella alta. A third method for judging patella alta is that described by Laurin and associates, 43 who used a lateral view roentgenogram with the knee flexed to 90°. The patella should lie under a line drawn across the anterior border of the femur. Patella alta suggests that the patella will engage the trochlea later in flexion and perhaps will be unstable. Standardized patellar roentgenographic views have been difficult to obtain because the patellofemoral relationship changes with the degree of
Fig. 6. The congruence (DAO) and sulcus (BAC) angles measured from roentgenogram obtained with knee at 45° of flexion. See text for detailed discussion. (From Merchant and colleagues.44 By permission of The Journal of Bone and Joint Surgery, Inc.)
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conjunction with a thorough clinical examination, provide complete evaluation of the patella and the patellofemoral joint. Rarely, such an evaluation may need to be supplemented by radionuclide scans, tomograms, or computed tomograms. REHABILITATION The rehabilitation program for patients with a patellofemoral pain syndrome is divided into four stages—acute, subacute, chronic, and maintenance. In the acute stage, the goals of rehabilitation are to control pain, inflammation, and irritation and to prevent muscle atrophy while maintaining aerobic fitness. During the acute phase, use of cryotherapy (ice packs), massage, and nonsteroidal anti-inflammatory medication is indicated to decrease pain and inflammation. Braces or orthoses, especially a patellar knee stabilizer or a foot orthosis if malalignment of the lower extremity is severe, can be prescribed. 45,46 Activities such as jumping, squatting, hill running, cycling, excessive stair climbing, or prolonged sitting with the knees flexed greater than 40° should be avoided. Specific exercises should be prescribed, including isometric exercises for the quadriceps and hip adductors as well as a pro-
longed stretching program for the hamstring and iliotibial band muscle groups. Toe raises and general range-of-motion exercises for the knee are also begun in this stage. If application of ice does not relieve pain, transcutaneous electrical nerve stimulation or high-intensity galvanic stimulation may be attempted. In the subacute phase of rehabilitation, the goals are to increase strength and flexibility, to protect the patellar surface, and to do 30 minutes of exercises two to three times daily. Usually, patients are advanced to this phase of the rehabilitation program when they have minimal swelling, pain, and inflammation. Use of antiinflammatory measures, such as ice and nonsteroidal agents, is continued, and low-resistance strengthening exercises—multiple-angle isometrics or terminal knee-extension exercises from 0° to 30°—should be initiated. Patients should be taught to avoid hyperextension of the knee, as this position will often aggravate the symptoms. Usually at this time, flexibility exercises are increased, including prolonged pain-free static stretching of the hamstrings, quadriceps, heel cords, and lateral retinaculum. In the chronic phase of rehabilitation, the goals are to obtain maximal strength in the knee and to increase endurance training and range-ofmotion exercises. Patients progress to this stage when terminal knee-extension exercises can be done with 25- to 30-pound (11- to 14-kg) weights. Usually, patients are instructed to increase the motion of their quadriceps strengthening gradually (in 10° increments), as tolerated. In addition, patients are taught circuit weight training, isokinetic strengthening, and negative extension exercises with use of eccentric contraction of the quadriceps. Cardiovascular endurance exercises, such as bicycling, swimming, and a graduated running program, are emphasized during this stage. During the maintenance phase of rehabilitation, the goals are to return to any sport or activity slowly by developing the specific neuromuscular skills for that sport or activity. Exercises to continue strengthening, flexibility, and endurance training are maintained during this time, and the patient should continue to use ice after activities. During this stage, the patient should gradually return to unrestricted activities but should avoid deep-knee-squatting or knee-bending activities in the immediate future.
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SURGICAL INTERVENTION Elective surgical intervention in patients with anterior knee pain is highly dependent on recognition of the etiologic factor responsible for the pain. 47 In general, first-line, nonoperative treatment as described is effective in most patients. 2,48 Arthroscopy can play an important role in both the diagnosis and the treatment of knee pain. 49 When nonoperative modes of treatment fail, operative treatment can be considered. The operative treatment can be direct, such as chondrectomy,48 cartilage shaving, patellar resurfacing 50 and medial patellar ridge excision, or patellectomy.51,52 Indirect operative approaches include lateral retinacular release, 31,53 proximal realignment, 30 distal realignment, 28,29,50 or tibial tubercle elevation.19 In 1976, Goodfellow and colleagues 54 reported relief of pain in 18 of 23 patients who underwent chondrectomy after 2 years of nonoperative treatment for patellofemoral pain had failed. These carefully selected patients had a specific cartilage lesion, which they termed "basilar degeneration." They postulated that the source of pain was the abnormal stress in the subchondral bone. Of the five patients who had no improvement, two required patellectomy. In 1978, Bentley 55 compared four methods of surgical treatment of chondromalacia of the patella. He reviewed his experience with patients who had had 3 months of adequate conservative treatment but continued to have symptoms. Overall, he achieved satisfactory results in 25% after shaving of the patellar cartilage, in 35% after partial chondrectomy, in 60% after medial transfer of the patellar tendon, and in 77% after patellectomy. He concluded that cartilage excision and drilling were of benefit only in patients older than 20 years of age who had grade 1 or grade 2 changes. Adults with grade 3 changes and all patients with grade 4 changes should undergo patellectomy. Realignment procedures were recommended only for athletes and adolescents with grade 1, 2, or 3 changes. In 1983, McCarroll and associates 58 discussed the results achieved in 184 knees treated by a variety of procedures. In knees with grade 2 or grade 3 chondromalacia, a trephine and drilling procedure produced 70% satisfactory results, whereas shaving yielded only 56% satisfactory results in similar patients. Facetectomy yielded satisfactory results in patients with grade 4 disease.
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When chronic lateral subluxation is diagnosed, lateral retinacular release should be contemplated. 53 In patients with grade 1 or grade 2 disease, Osborne and Fulford 57 found 87% satisfactory results after 1-year follow-up. At 3-year follow-up, however, the outcome diminished to 37% satisfactory results. Crosby and Insall 29 reported a 75% satisfactory rate with proximal realignment and no evidence of osteoarthritis on roentgenograms after 8 years of follow-up. Distal realignment procedures were less successful in their experience (satisfactory results in only 59% and, more importantly, degenerative changes in 70% of those patients). Elevation of the tibial tubercle was devised in an effort to increase the extensor mechanism moment arm and decrease stresses across the patellofemoral joint. Maquet 19 described this procedure as a 2-cm elevation of the tibial tubercle and stated that forces on the patellofemoral joint were decreased by approximately 50%. Ferguson and colleagues 20 claimed that a 1.3-cm elevation would result in an 83.5% reduction of forces. In their report of 88 patients with anterior knee pain, results of the Maquet procedure were 84% satisfactory. We believe that results of surgical intervention are most advantageous when both the extent of articular damage and malalignment are assessed and treated. Thus, operative intervention should be directed toward the anatomic abnormality. Not surprisingly, other investigators have shown that the best results of surgical intervention correlate with lack of patella alta, a normal sulcus angle, and a "Q" angle that is less than 20°. CONCLUSION For patients with anterior knee pain, we recommend careful physical and radiographic examination followed by adequate first-line, nonoperative intervention, including strengthening, nonsteroidal anti-inflammatory medications, ice, and bracing. If these measures fail, cautious surgical intervention should be directed toward the area of anatomic abnormality. REFERENCES
1. Sisk TD: Knee injuries. In Campbell's Operative Orthopaedics. Vol 3. Seventh edition. Edited by AH Crenshaw. St. Louis, CV Mosby Company, 1987, pp 2283-2496 2. Sandow MJ, Goodfellow JW: The natural history of anterior knee pain in adolescents. J Bone Joint Surg [Br] 67:36-38,1985
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3. Radin EL: Chondromalacia: treatment based on a more precise diagnosis. In Chondromalacia of the Patella. Edited by JC Pickett, EL Radin. Baltimore, Williams & Wilkins, 1983, pp 134-143 4. Hollinshead WH: Anatomy for Surgeons. Vol 3: The Back and Limbs. Second edition. New York, Harper & Row, Publishers, 1969 5. Hungerford DS, Barry M: Biomechanics of the patellofemoral joint. Clin Orthop 144:9-15, 1979 6. Reider B, Marshall JL, Koslin B, Ring B, Girgis FG: The anterior aspect of the knee joint: an anatomical study. J Bone Joint Surg [Am] 63:351-356,1981 7. Wiberg G: Roentgenographic and anatomic studies on the femoropatellar joint: with special reference to chondromalacia patellae. Acta Orthop Scand 12:319-410,1941 8. Casscells SW: Gross pathological changes in the knee joint of the aged individual: a study of 300 cases. Clin Orthop 132:225-232, 1978 9. Goodfellow J, Hungerford DS, Zindel M: Patello-femoral joint mechanics and pathology. 1. Functional anatomy of the patello-femoral joint. J Bone Joint Surg [Br] 58:287-290, 1976 10. Lieb FJ, Perry J: Quadriceps function: an anatomical and mechanical study using amputated limbs. J Bone Joint Surg [Am] 50:1535-1548,1968 11. Hallisey MJ, Doherty N, Bennett WF, Fulkerson JP: Anatomy of the junction of the vastus lateralis tendon and the patella. J Bone Joint Surg [Am] 69:545-549,1987 12. Larson RL, Jones DC: Dislocations and ligamentous injuries of the knee. In Fractures in Adults. Vol 2. Second edition. Edited by CA Rockwood Jr, DP Green. Philadelphia, JB Lippincott Company, 1984, pp 1480-1591 13. Warren LF, Marshall JL: The supporting structures and layers on the medial side of the knee. J Bone Joint Surg [Am] 61:56-62,1979 14. Fulkerson JP, Gossling HR: Anatomy of the knee joint lateral retinaculum. Clin Orthop 153:183-188, 1980 15. Seebacher JR, Inglis AE, Marshall JL, Warren RF: The structure of the posterolateral aspect of the knee. J Bone Joint Surg [Am] 64:536-541, 1982 16. Boland AL: Soft tissue injuries of the knee. In The Lower Extremity and Spine in Sports Medicine. Edited by JA Nicholas, EB Hershman. St. Louis, CV Mosby Company, 1986, pp 983-1012 17. Reilly DT, Martens M: Experimental analysis of the quadriceps muscle force and patello-femoral joint reaction force for various activities. Acta Orthop Scand 43:126-137,1972 18. Huberti HH, Hayes WC: Patellofemoral contact pressures: the influence of Q-angle and tendofemoral contact. J Bone Joint Surg [Am] 66:715-724,1984 19. Maquet P: Mechanics and osteoarthritis of the patellofemoral joint. Clin Orthop 144:70-73, 1979 20. Ferguson AB Jr, Brown TD, Fu FH, Rutkowski R: Relief of patellofemoral contact stress by anterior displacement of the tibial tubercle. J Bone Joint Surg [Am] 61:159-166, 1979 21. Insall J: Patellar pain. J Bone Joint Surg [Am] 64:147152,1982 22. Jackson RW: Etiology of chondromalacia patellae. Instr Course Lect 25:36-40, 1976 23. Mankin HJ: Biochemical and metabolic aspects of osteoarthritis. Orthop Clin North Am 2:19-31, March 1971 24. Ficat P: Lateral fascia release and lateral hyperpressure syndrome. In Chondromalacia of the Patella. Edited by JC Pickett, EL Radin. Baltimore, Williams & Wilkins, 1983, pp 95-112 25. Casscells SW: Chondromalacia patella and its relationship to anterior femoral pain. In Chondromalacia of the
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32. 33.
34. 35. 36. 37. 38. 39. 40.
41. 42. 43. 44. 45. 46. 47. 48. 49. 50.
Patella. Edited by JC Pickett, EL Radin. Baltimore, Williams & Wilkins, 1983, pp 83-94 Cofield RH, Bryan RS: Acute dislocation of the patella: results of conservative treatment. J Trauma 17:526-530, 1977 Hawkins RJ, Bell RH, Anisette G: Acute patellar dislocations: the natural history. Am J Sports Med 14:117120,1986 Hughston JC, Walsh WM: Proximal and distal reconstruction of the extensor mechanism for patellar subluxation. Clin Orthop 144:36-42, 1979 Crosby EB, Insall J: Recurrent dislocation of the patella: relation of treatment to osteoarthritis. J Bone Joint Surg [Am] 58:9-13,1976 Insall J, Falvo KA, Wise DW: Chondromalacia patellae: a prospective study. J Bone Joint Surg [Am] 58:1-8,1976 Larson RL, Cabaud HE, Slocum DB, James SL, Keenan T, Hutchinson T: The patellar compression syndrome: surgical treatment by lateral retinacular release. Clin Orthop 134:158-167, 1978 Ogden JA, McCarthy SM, Jokl P: The painful bipartite patella. J Pediatr Orthop 2:263-269,1982 Batten J, Menelaus MB: Fragmentation of the proximal pole of the patella: another manifestation of juvenile traction osteochondritis? J Bone Joint Surg [Br] 67:249251, 1985 Outerbridge RE: The etiology of chondromalacia patellae. J Bone Joint Surg [Br] 43:752-757, 1961 Wiles P, Andrews PS, Devas MB: Chondromalacia of the patella. J Bone Joint Surg [Br] 38:95-113,1956 Heine J: Über die Arthritis deformans. Virchows Arch Pathol Anat 260:521-663, 1926 Casscells SW: Chondromalacia of the patella. J Pediatr Orthop 2:560-564, 1982 Björkström S, Goldie IF, Wetterqvist H: Intramedullary pressure of the patella in chondromalacia. Arch Orthop Trauma Surg 97:81-85, 1980 Rydholm A: Pseudochondromalacia patellae. Acta Orthop Scand 49:205-210, 1978 Millbauer DL, Patel S: Roentgenographic examination of the knee. In The Lower Extremity and Spine in Sports Medicine. Edited by JA Nicholas, EB Hershman. St. Louis, CV Mosby Company, 1986, pp 801-840 Blumensaat C: Die Lageabweichungen und Verrenkungen der Kniescheibe. Ergeb Chir Orthop 31:149-223, 1938 Insall J, Goldberg V, Salvati E: Recurrent dislocation of the high-riding patella. Clin Orthop 88:67-69,1972 Laurin CA, Levesque HP, Dussault R, Labelle H, Peides JP: The abnormal lateral patellofemoral angle. J Bone Joint Surg [Am] 60:55-60,1978 Merchant AC, Mercer RL, Jacobsen RH, Cool CR: Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg [Am] 56:1391-1396,1974 Palumbo PM Jr: Dynamic patellar brace: a new orthosis in the management of patellofemoral disorders; a preliminary report. Am J Sports Med 9:45-49, 1981 Villar RN: Patellofemoral pain and the infrapatellar brace: a military view. Am J Sports Med 13:313-315,1985 Radin EL: Anterior knee pain: the need for a specific diagnosis, stop calling it chondromalacia! Orthop Rev 14:128-134,1985 Gruber MA: The conservative treatment of chondromalacia patellae. Orthop Clin North Am 10:105-115, January 1979 Dandy DJ: Arthroscopy in the treatment of young patients with anterior knee pain. Orthop Clin North Am 17:221-229, April 1986 Insall J, Tria AJ, Aglietti P: Resurfacing of the patella. J Bone Joint Surg [Am] 62:933-936,1980
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51. Compere CL, Hill JA, Lewinnek GE, Thompson RG: A new method of patellectomy for patellofemoral arthritis. J Bone Joint Surg [Am] 61:714-719, 1979 52. Kelly MA, Insall JN: Patellectomy. Orthop Clin North Am 17:289-295, April 1986 53. Metcalf RW: An arthroscopic method for lateral release of the subluxating or dislocating patella. Clin Orthop 167:9-18,1982 54. Goodfellow J, Hungerford DS, Woods C: Patello-femoral joint mechanics and pathology. 2. Chondromalacia patellae. J Bone Joint Surg [Br] 58:291-299,1976
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55. Bentley G: The surgical treatment of chondromalacia patellae. J Bone Joint Surg [Br] 60:74-81,1978 56. McCarroll JR, O'Donoghue DH, Grana WA: The surgical treatment of chondromalacia of the patella. Clin Orthop 175:130-134, 1983 57. Osborne AH, Fulford PC: Lateral release of chondromalacia patellae. J Bone Joint Surg [Br] 64:202-205,1982
MICHAEL H. BOURNE, M.D., WILLIAM A. HAZEL, Jr., M.D., Department of Orthopedics; STEVEN G. SCOTT, D.O., Department of Physical Medicine and Rehabilitation; FRANKLIN H. SIM, M.D., Department of Orthopedics Anterior knee pain is a common symptom, especially in adolescence, and often no specific cause is sought or identified. Physicians who treat patients with knee pain should understand the normal anatomic features and the biomechanics of the patellofemoral joint. We review this information and discuss important aspects of the physical examination and roentgenographic evaluation in patients with anterior knee pain. Once the clinical cause of anterior knee pain has been established, directed nonoperative treatment including physical therapy should be initiated. Surgical intervention is generally reserved for patients in whom nonoperative management is unsuccessful and identifiable abnormalities exist.
Anterior knee pain is a frequent source of impairment. 1 Although the cause of such pain often remains unknown and the condition may be selflimited, 2 a specific diagnosis should be sought and appropriate treatment initiated. 3 ANATOMY The patella is the largest sesamoid bone in the human skeleton, and its undersurface possesses the thickest articular cartilage. 4 Primary ossification of the patella normally begins at age 4 to 6 years. The patella has three primary functions: (1) it increases the lever arm of the quadriceps mechanism, (2) it protects the anterior aspect of the knee, and (3) it enhances the cosmesis of the lower extremity. Normal joint function necessitates stability and strength. Static stability of the patellofemoral joint is provided by bony congruence between the patella and the trochlea of the femur, which varies with the position of knee flexion.5
Address reprint requests to Dr. F. H. Sim, Department of Orthopedics, Mayo Clinic, Rochester, MN 55905. Mayo Clin Proc 63:482-491,1988
Several ligamentous structures contribute to static stability, and the extensor mechanism provides strength and dynamic stability. 6 The articular anatomy of the patella is straightforward. The medial and lateral facets are separated by a vertical ridge. 4 A smaller facet, known as the odd facet, exists medially and is delineated by a second vertical ridge. Wiberg7 has classified patellar shapes. Most commonly, the lateral facet is larger than the medial facet, and both are concave. The corresponding femoral trochlear groove is also variable in shape and configuration. It may be broad and shallow or more V-shaped. 8 Therefore, the patellofemoral joints are inherently more stable in some persons than in others. During motion, the patella glides 7 to 8 cm with respect to the femur.7 When the knee is extended, the patella is at its most proximal point, but it does not seat into the trochlea until approximately 20° of flexion, at which point its most distal aspect contacts the trochlea. With further flexion, the patella slides distally and the contact areas become more proximal on the patella. At full flexion, only the most medial and lateral aspects of the proximal patella contact the femur.9
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The quadriceps mechanism h a s been well described anatomically (Fig. I). 6 It inserts in a multilaminar fashion. Superficially, the rectus femoris inserts anteriorly on the patella. A middle layer consists of the vastus lateralis and vastus medialis. The medial portion of the distal vastus medialis, known as the vastus medialis obliquus, inserts into the upper medial pole of the patella at an angle of 55° to 70° from the vertical. 10 Recently, the distal portion of the vastus lateralis has been described as the vastus lateralis obliquus. 11 Because the quadriceps muscle is aligned anatomically with the shaft of the femur and not with the mechanical axis of the lower extremity, a dynamic lateral force is applied to the patella during extension of the knee. 12 The importance of the vastus medialis obliquus is that it provides the only dynamic medial stability for the patella. 10 The ligamentous structures of the patellofemoral joint are complex. The medial and lateral retinacula form from structures in the first and second layers of the knee joint. 13,14 It is probably simplest to think of them as winglike structures
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that connect the patella to the femur, the menisci, and the tibia both medially and laterally. Within these wings are areas of condensation that form the patellofemoral ligaments. This patellar retinaculum is particularly important laterally, where it also inserts into the hamstring musculature; 15 hence, tightened hamstrings can lead to patellofemoral symptoms. Finally, several bursae are present around the knee joint (Fig. 2).16 The bursae and the anterior fat pad may give rise to a variety of syndromes that mimic patellofemoral disease. It is important to examine the knee to identify these sources of pain. BIOMEOHANICS An understanding of the patellofemoral joint biomechanics is essential to understanding pathologic conditions of the knee. Reilly and Martens, 17 among others, have examined the patellofemoral contact forces under a variety of loading conditions. 5,18 When the knee is extended from 90° of flexion to the neutral position against 9 kg of constant resistance, the patellofemoral reaction
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force is maximal at 90° and declines to 0 at full extension. Conversely, the quadriceps tendon force, which is minimal at full flexion, increases dramatically as full extension is attained. When a weight is hung from the foot and the knee is extended, the maximal patellofemoral forces are attained at approximately 36° of flexion; again, however, the quadriceps muscle force increases near full extension. During deep-knee-bending conditions, the patellofemoral force increases with flexion, as does the quadriceps force. The pertinent biomechanics can be summarized as follows: near full extensions, the patellofemoral force is 0; during stair climbing, it can increase to 3.3 times the body weight; and with deep knee bends, forces approaching 8 times the body weight can be attained. 17 When the knee is moved through a range of motion against resistance, maximal patellofemoral forces are found between 35° and 40° of flexion.5'17 A direct relationship exists between the patellofemoral contact pressure and the function of the patella as a lever arm for knee extension. 19 Near full extension, the patella rides close to the shaft and the center of rotation of the knee and therefore provides a minimal lever arm for extension. With flexion, the patella rides up and over the trochlea and displaces the patellar tendon away from the instant center of rotation. This movement provides an increased mechanical advantage to the quadriceps tendon but also increases proportionately the patellofemoral contact pressure. The work of Maquet 19 and others 2& has demonstrated that elevation of the tibial tubercle results in decreased quadriceps and patellofemoral contact forces. From a geometric perspective, as shown in Figure 3, elevation of the tubercle increases the angles between the quadriceps tendon and the patellar tendon. With application of the parallelogram rule, when a larger angle is subtended, the resultant posteriorly directed force is decreased. The clinical significance of this principle will be discussed subsequently in this article. ETIOLOGIC FACTORS Anterior knee pain may be attributed to several sources, 21 including the synovium, periarticular structures, and lastly bone. Because articular cartilage is aneural, it cannot be implicated as a primary source of patellofemoral pain.
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Fig. 3. Patellofemoral contact force (Fc) is reduced with elevation of patellar tendon insertion. Fp = force of patellar tendon; Fq = force of quadriceps tendon. (From Ferguson and associates. 20 By permission of The Journal of Bone and Joint Surgery, Inc.)
Jackson 2 has implicated both biochemical and biomechanical causes for anterior knee pain. The two may not be mutually exclusive.23 Biomechanical factors can produce fissures and erosion on the articular surface. The release of lysosomal enzymes from any cause stimulates an ensuing synovial inflammation and results in pain and degradation of articular cartilage. 24 Although it has not been proved, some investigators have suggested that debridement of damaged tissue may decrease the production of lysosomal enzymes. 25 Rheumatic disease should be included when synovial sources of pain are considered. Biomechanical causes of anterior knee pain can be acute or chronic events. Acute events include dislocation of the patella, 26,27 patellar fracture, or bursitis. Chronic sources include recurrent patellar subluxation, 12,28,29 malalignment, 30 excessive lateral pressure syndrome, 31 meniscal injury, and traction epiphysitis, possibly accounting for Osgood-Schlatter disease, Larsen-Johansson disease, bipartite patella, 32 and proximal pole traction osteochondritis. 33
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Cartilaginous defects of the patella can be classified by location, occurring on the lateral, medial, or odd facet or as central defects along the median ridge. They can also be bipolar, involving both medial and lateral facets with a normal ridge, or they can be global. Lesions can be graded on the basis of distinguishing features on arthroscopic examination. Grade 1 lesions demonstrate softening and discoloration of the cartilage, grade 2 lesions show fibrillation and Assuring less than 1.3 cm in diameter, whereas grade 3 lesions show similar fibrillation involving an area not greater than 2.3 cm. Grade 4 lesions are evidenced by full-thickness cartilage loss with a mirror lesion on the femur.34 Cartilaginous lesions of the patella are ubiquitous and partially dependent on age. Wiles and associates 35 reported that they exist in only 26% of those younger than 20 years of age but in 75% of those between 20 and 29 years, 85% of those between 30 and 39 years, and in 100% of persons older than 50 years of age. In contrast, Heine 36 found an 80% rate of degeneration in the patella in the 50- to 59-year-old age group. More recently, Casscells 8 examined 300 knees in patients with a mean age of 70 years and found 58% with normal cartilage or grade 1 lesions of the patella. The presence of a lesion per se does not invariably correlate with symptoms. 37 In several studies, less than 50% of patients with lesions at arthrotomy were found to be symptomatic. 33 Furthermore, the development of changes on the patella seems to be clinically distinct from the onset of osteoarthritis. 9 Therefore, we believe that the term "chondromalacia" is vague, uncertain, and not useful as a diagnostic classification. It is a descriptive term that should be reserved for recording findings at the time of arthrotomy or arthroscopy. When cartilage has been damaged, its loadcarrying capacity is diminished and there is increased load transmission to the subchondral bone. This increased pressure might be the source of anterior knee pain. In 1980, Björkström and colleagues 38 found elevated intramedullary patellar pressures in patients with anterior knee pain in comparison with control subjects. The mean pressure of those with anterior knee pain was 44 mm Hg in comparison with 19 mm Hg in the control knees. Malalignment may cause a lateral compression syndrome that results in anterior knee pain. Sev-
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eral studies, however, have shown that a strong relationship between chondromalacia patellae and patella alta or between anterior knee pain and congruence and sulcus angles does not always exist. Traumatic injuries such as intraarticular fractures or osteochondritis dissecans are well-known causes of chronic knee pain. Other reasons for anterior knee pain are inflammation of various bursae, inflammation of the infrapatellar fat pad, avascular necrosis, synovial inflammation, impingement, 21 pseudochondromalacia patellae, 39 or plica syndrome. In some patients, no cause of anterior knee pain can be identified. In a follow-up study of a large group of adolescent girls with knee pain but no detectable abnormalities, Sandow and Goodfellow2 found that, at a mean of 4 years, most had persistent pain but few were restricted in activities or used analgesics. PHYSICAL EXAMINATION Physical examination of the patella is an integral part of the complete knee evaluation. The normal and the abnormal knee should always be compared and contrasted. A detailed history will complement and help direct the physical examination. Often patients will experience pain during prolonged sitting (positive theater sign), stair climbing, and knee-bending activities. Thorough examination of the knee is a complex task that should include evaluation of the foot, ankle, knee, and hip as well. We will discuss examination of the patellofemoral joint in detail. As an initial step, the varus or valgus alignment of the knee should be noted. A convenient measurement is the "Q" angle or that angle formed by a line between the center of the patella extending proximally to the anterosuperior iliac spine and extending distally to the center of the tibial tubercle (Fig. 4). Normally, this is less than 10° in men and 15° in women. 40 An excessive "Q" angle predisposes to lateral patellar subluxation or dislocation. The patient should be observed standing with the feet together and sitting with the knees flexed to 90° to determine the orientation of the patella with respect to the coronal plane. The patella may be internally rotated ("squinting") or externally rotated ("grasshopper eyes"), the position depending on femoral or tibial malrotation. Patellar motion should be observed while the patient is walking. Comparison of the quadriceps circumference at 10 cm proximal to
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Palpation of the patella may elicit crepitus or subluxation, which may or may not be painful. The patella is divided into longitudinal quadrants, and subluxation should be attempted both medially and laterally. Displacement of more than two quadrants (half of the patella) over the medial or lateral aspect is considered abnormal. Appreciable patient anxiety during attempted lateral subluxation is termed a "positive apprehension test" and is a sign of probable subluxation or past dislocation of the patella. Rarely, the patella can be completely dislocated at the time of examination. Excessive tilting of the medial or lateral aspect of the patella is evidence of laxity in the retinaculum.
Anterior superior iliac spine
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Fig. 4. The "Q" angle (or quadriceps angle), formed by extension of lines drawn from center of patella proximally to anterosuperior iliac spine and distally to tibial tubercle, denotes alignment of the knee. Excessive "Q" angle predisposes to lateral patellar subluxation or dislocation.
the medial joint line will often reflect subtle signs of quadriceps atrophy, particularly with respect to the vastus medialis obliquus. In patients with an acute patellar injury, this atrophy is usually not present. When the knee is fully extended and the quadriceps is relaxed, the patella should be fairly mobile. With flexion at 20°, the patella engages the trochlea, and structures on both the medial and lateral aspects of the knee begin to tighten. Tenderness or palpable defects in the retinaculum may be noted, and patella alta or baja may also be diagnosed with the knee in slight flexion.
RADIOGRAPHIC EXAMINATION In the past, radiographic examination of the patella and the patellofemoral joint has been hampered because standardized views have not been used. Familiarity with the variety of roentgenographic techniques used in evaluation of the patellofemoral joint is useful. On a plain anteroposterior film, the "Q" angle or quadriceps angle can be measured by using the angle formed by extending lines through the femoral shaft and the tibial tubercle to the center of the patella (Fig. 4). The "Q" angle can also be determined on clinical examination as the angle formed from lines drawn from the anterosuperior iliac spine to the center of the patella and from the center of the patella to the tibial tubercle with the knee in full extension. An increased "Q" angle suggests increased lateral pressure and possible subluxation. A lateral roentgenographic view is helpful in determining a second important criterion of patellar position—that is, its relative height, proximal or distal to the tibial tubercle. This characteristic has been termed, respectively, patella "alta" or patella "baja" and can be analyzed in several ways. Blumensaat 41 devised a test in which a lateral view roentgenogram obtained with the knee flexed to 30° is used. When the distal pole of the patella rides above the intercondylar condensation, patella alta exists. Perhaps more familiar and more accurate is the ratio described by Insall and co-workers,42 in which the height of the patella should be equal to the height of the patellar tendon (Fig. 5). This relationship is maintained for flexion from 20° to 70°. The
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knee flexion. Full flexion is used for a "sunrise" or "sunset" view, but the patella is well engaged in the trochlea at these points. Merchant and colleagues 44 began using 45° of flexion and devised the congruence angle (Fig. 6). The sulcus angle, which averages 138°, is that angle between tangents across the lateral and medial condyles (angle BAC in Figure 6). A line that bisects this sulcus angle (line OA in Figure 6) is used as a reference to a line drawn to the inferior portion of the patella (line DA). The angle formed (DAO in Figure 6) is termed the "congruence angle" and is normally -6° (being negative on the medial side and positive on the lateral side). An angle greater than 11° is outside the standard deviation and is considered to show lateral subluxation. A fourth measurement that is useful for determining patellar position was devised by Laurin and others. 43 With the knee flexed to 20°, the patella is just beginning to engage the trochlea and is at its position of maximal instability. The patellofemoral angle on the lateral aspect is then measured, as shown in Figure 7; if that angle is neutral (that is, the lines are parallel) or it opens medially, this finding is pathognomonic of lateral patellar tightness and subluxation. Thus, these four measurements—the "Q" angle, patella alta with use of the Insall ratio, the congruence and sulcus angles of Merchant, and the lateral patellofemoral angle of Laurin—in Fig. 5. The Insall ratio for determining relative patellar height. In normal knee, height of patella (P) should equal height of patellar tendon (PT).
length of the patellar tendon can slightly exceed the patellar height, but any ratio beyond 1.2 (tendon to patella) is considered abnormal and is suggestive of patella alta. A third method for judging patella alta is that described by Laurin and associates, 43 who used a lateral view roentgenogram with the knee flexed to 90°. The patella should lie under a line drawn across the anterior border of the femur. Patella alta suggests that the patella will engage the trochlea later in flexion and perhaps will be unstable. Standardized patellar roentgenographic views have been difficult to obtain because the patellofemoral relationship changes with the degree of
Fig. 6. The congruence (DAO) and sulcus (BAC) angles measured from roentgenogram obtained with knee at 45° of flexion. See text for detailed discussion. (From Merchant and colleagues.44 By permission of The Journal of Bone and Joint Surgery, Inc.)
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conjunction with a thorough clinical examination, provide complete evaluation of the patella and the patellofemoral joint. Rarely, such an evaluation may need to be supplemented by radionuclide scans, tomograms, or computed tomograms. REHABILITATION The rehabilitation program for patients with a patellofemoral pain syndrome is divided into four stages—acute, subacute, chronic, and maintenance. In the acute stage, the goals of rehabilitation are to control pain, inflammation, and irritation and to prevent muscle atrophy while maintaining aerobic fitness. During the acute phase, use of cryotherapy (ice packs), massage, and nonsteroidal anti-inflammatory medication is indicated to decrease pain and inflammation. Braces or orthoses, especially a patellar knee stabilizer or a foot orthosis if malalignment of the lower extremity is severe, can be prescribed. 45,46 Activities such as jumping, squatting, hill running, cycling, excessive stair climbing, or prolonged sitting with the knees flexed greater than 40° should be avoided. Specific exercises should be prescribed, including isometric exercises for the quadriceps and hip adductors as well as a pro-
longed stretching program for the hamstring and iliotibial band muscle groups. Toe raises and general range-of-motion exercises for the knee are also begun in this stage. If application of ice does not relieve pain, transcutaneous electrical nerve stimulation or high-intensity galvanic stimulation may be attempted. In the subacute phase of rehabilitation, the goals are to increase strength and flexibility, to protect the patellar surface, and to do 30 minutes of exercises two to three times daily. Usually, patients are advanced to this phase of the rehabilitation program when they have minimal swelling, pain, and inflammation. Use of antiinflammatory measures, such as ice and nonsteroidal agents, is continued, and low-resistance strengthening exercises—multiple-angle isometrics or terminal knee-extension exercises from 0° to 30°—should be initiated. Patients should be taught to avoid hyperextension of the knee, as this position will often aggravate the symptoms. Usually at this time, flexibility exercises are increased, including prolonged pain-free static stretching of the hamstrings, quadriceps, heel cords, and lateral retinaculum. In the chronic phase of rehabilitation, the goals are to obtain maximal strength in the knee and to increase endurance training and range-ofmotion exercises. Patients progress to this stage when terminal knee-extension exercises can be done with 25- to 30-pound (11- to 14-kg) weights. Usually, patients are instructed to increase the motion of their quadriceps strengthening gradually (in 10° increments), as tolerated. In addition, patients are taught circuit weight training, isokinetic strengthening, and negative extension exercises with use of eccentric contraction of the quadriceps. Cardiovascular endurance exercises, such as bicycling, swimming, and a graduated running program, are emphasized during this stage. During the maintenance phase of rehabilitation, the goals are to return to any sport or activity slowly by developing the specific neuromuscular skills for that sport or activity. Exercises to continue strengthening, flexibility, and endurance training are maintained during this time, and the patient should continue to use ice after activities. During this stage, the patient should gradually return to unrestricted activities but should avoid deep-knee-squatting or knee-bending activities in the immediate future.
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SURGICAL INTERVENTION Elective surgical intervention in patients with anterior knee pain is highly dependent on recognition of the etiologic factor responsible for the pain. 47 In general, first-line, nonoperative treatment as described is effective in most patients. 2,48 Arthroscopy can play an important role in both the diagnosis and the treatment of knee pain. 49 When nonoperative modes of treatment fail, operative treatment can be considered. The operative treatment can be direct, such as chondrectomy,48 cartilage shaving, patellar resurfacing 50 and medial patellar ridge excision, or patellectomy.51,52 Indirect operative approaches include lateral retinacular release, 31,53 proximal realignment, 30 distal realignment, 28,29,50 or tibial tubercle elevation.19 In 1976, Goodfellow and colleagues 54 reported relief of pain in 18 of 23 patients who underwent chondrectomy after 2 years of nonoperative treatment for patellofemoral pain had failed. These carefully selected patients had a specific cartilage lesion, which they termed "basilar degeneration." They postulated that the source of pain was the abnormal stress in the subchondral bone. Of the five patients who had no improvement, two required patellectomy. In 1978, Bentley 55 compared four methods of surgical treatment of chondromalacia of the patella. He reviewed his experience with patients who had had 3 months of adequate conservative treatment but continued to have symptoms. Overall, he achieved satisfactory results in 25% after shaving of the patellar cartilage, in 35% after partial chondrectomy, in 60% after medial transfer of the patellar tendon, and in 77% after patellectomy. He concluded that cartilage excision and drilling were of benefit only in patients older than 20 years of age who had grade 1 or grade 2 changes. Adults with grade 3 changes and all patients with grade 4 changes should undergo patellectomy. Realignment procedures were recommended only for athletes and adolescents with grade 1, 2, or 3 changes. In 1983, McCarroll and associates 58 discussed the results achieved in 184 knees treated by a variety of procedures. In knees with grade 2 or grade 3 chondromalacia, a trephine and drilling procedure produced 70% satisfactory results, whereas shaving yielded only 56% satisfactory results in similar patients. Facetectomy yielded satisfactory results in patients with grade 4 disease.
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When chronic lateral subluxation is diagnosed, lateral retinacular release should be contemplated. 53 In patients with grade 1 or grade 2 disease, Osborne and Fulford 57 found 87% satisfactory results after 1-year follow-up. At 3-year follow-up, however, the outcome diminished to 37% satisfactory results. Crosby and Insall 29 reported a 75% satisfactory rate with proximal realignment and no evidence of osteoarthritis on roentgenograms after 8 years of follow-up. Distal realignment procedures were less successful in their experience (satisfactory results in only 59% and, more importantly, degenerative changes in 70% of those patients). Elevation of the tibial tubercle was devised in an effort to increase the extensor mechanism moment arm and decrease stresses across the patellofemoral joint. Maquet 19 described this procedure as a 2-cm elevation of the tibial tubercle and stated that forces on the patellofemoral joint were decreased by approximately 50%. Ferguson and colleagues 20 claimed that a 1.3-cm elevation would result in an 83.5% reduction of forces. In their report of 88 patients with anterior knee pain, results of the Maquet procedure were 84% satisfactory. We believe that results of surgical intervention are most advantageous when both the extent of articular damage and malalignment are assessed and treated. Thus, operative intervention should be directed toward the anatomic abnormality. Not surprisingly, other investigators have shown that the best results of surgical intervention correlate with lack of patella alta, a normal sulcus angle, and a "Q" angle that is less than 20°. CONCLUSION For patients with anterior knee pain, we recommend careful physical and radiographic examination followed by adequate first-line, nonoperative intervention, including strengthening, nonsteroidal anti-inflammatory medications, ice, and bracing. If these measures fail, cautious surgical intervention should be directed toward the area of anatomic abnormality. REFERENCES
1. Sisk TD: Knee injuries. In Campbell's Operative Orthopaedics. Vol 3. Seventh edition. Edited by AH Crenshaw. St. Louis, CV Mosby Company, 1987, pp 2283-2496 2. Sandow MJ, Goodfellow JW: The natural history of anterior knee pain in adolescents. J Bone Joint Surg [Br] 67:36-38,1985
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