GERALD McGINTY, MS, PT, SCS Keesler Medical Center JAMES J. IRRGANG, PhD, PT, ATC University of Pittsburgh

The extensor mechanism of the knee in- tions: the vastus medialis longus and the vastus cludes the four muscles of the quadriceps, the medialis obliquus (Figure 1). patella, the patellar tendon, all the soft tissues The rectus femoris originates fromthe an- attaching to the pa- terior inferior iliac spine and groove superior to tella, and the tibia1 tu- the acetabulum and inserts into the quadriceps berosity (Gressamer& tendon. The fibers of the rectus femoris are ori- McConnell, 1998).It is ented about 5" relative to the long axis of the involved with almost femur. It is the only one of the quadriceps any functional activity muscles to cross the hip joint, giving the hip of the lower extremity. joint some importance with respect to the ex- Disorders of the ex- tensor mechanism. A shortened rectus femoris tensor mechanism are might inhibit full excursion of the patella on the some of the most trochlea as the knee flexes, particularly when common conditions the hip is extended (McConnell, 1986). presenting to clini- The vastus intermedius originatesfrom the ectivelyrec cians managing sports anterior and lateral surfaces of the body of the

s. injuries. Although the femur and inserts into the quadriceps tendon. Malalianmentotthe patellaand incidence of these dis- The direction of pull of the vastus intermedius hyperionation of the rubtalarjoint orders is high, the di- is along the line of the femur. It functions as aretommc mly (orrelat~d with n in agnosis and treatment the most efficient extensor, requiring less force are often difficult. The to extend the knee than do the other parts of

KeyVVUIU~: k~luu, paiu~~u~u~~~u~ar purpose of this article the quadriceps (Lieb & Perry, 1968). pain.expn is to discuss the anat- The vastus lateralis originates from the omy and biomechan- greater trochanter and lateral lip of the linea ics of the extensor mechanism.Hopefully, this aspera of the femur. It inserts anteriorly into knowledge will help athletic trainers and thera- the quadriceps tendon and laterally into the lat- pists diagnose and treat these disorders. eral retinaculum. The fibers of the vastus lateralis are oriented 20 to 40" relative to the long axis of the femur, with the distal fibers more obliquely oriented than the proximal fibers. The dynamic structures of the extensor mecha- The vastus medialis longus originates from

nism are the quadriceps-m muscles. - The+q~adri:_*~",thefntertrochanteric line and media __,__* - ___X-C,r >"- ICI--I"-I--L ------* -- ceps consists of the rectus femoris, the vastus linea aspera of the femur and insert intermedius,the vastus lateralis, and thevastus into the quadriceps tendon. The fibers of the medialis (Williams & Warwick, 1980). The vastus medialis longus are oriented 15 to 18" vastus medialis can be divided into two por- relative to the long axis of the femur.

a 2000Human Kinetics. ATT 5(5). pp. 6-11 6 1 SEPTEMBER2000 ATHLETICTHERAPY TODAY The quadriceps muscles function as extensors of the leg in the open kinetic chain (OKC) and as decel- erators of the leg in the closed kinetic chain (CKC). During OKC knee extension, the flexion moment arm increases as the leg moves into extension, requiring the quadriceps force to increase as the knee extends. During CKC exercise, the flexion moment arm in- creases as the leg moves into flexion, requiring the quadriceps force to increase as the knee flexes. The VMO, although active during leg extension, is not capable of performing independent extension of the leg. The VMO is the primary dynamic stabi- lizer of the patella, helping keep it centered in the trochlea of the femur. The centered position provided by the VMO enhances the efficiency of the quadri- ceps during knee extension. Historically, treatment of patellofemoral pain has focused on strengthening the VMO to improve dynamic patellar stability. How- Medial retinaculum Lateral retinaculum ever, there is no conclusive evidence that specific exercises can be performed to selectively recruit the VMO (Powers, 1998).

QclrisdaicsprTendon

Figure 1 Angle of pull of the quadriceps femoris muscles. The quadriceps tendon is formed by the convergence Reprinted with permission of W.B. Saunders from McConnell, J.,& of the quadriceps muscles. The tendon is composed Fulkerson, J. (1996). The knee: Patellofemoral and soft tissue inju- ries. In J.E. Zachazewski, D.J. Magee, & W.S. Quillen (Eds.), Athletic of three layers that insert into the patella (Williams & Warwick, 1980). The superficial layer contains the rectus femoris, which inserts into the superior pole and superior third of the anterior surface of the pa- The vastus medialis obliquus (VMO) originates tella. The intermediate layer contains the vastus from the tendons of the adductor magnus and lon- lateralis and vastus medialis and inserts into the base gus, as well as from the intermuscular septum, and of the patella posterior to the rectus femoris. The deep inserts into the medial retinaculumand superomedial layer contains the vastus intermedius, which inserts portion of the patella (Bose, Kanagasum, & Osman, into the base of the patella posterior to the other lay- 1980). The angle of insertion of the VMO into the ers but anterior to the capsule. patella is 50 to 55" off the long axis of the femur, making this portion of the quadriceps an effective The Patellar Ligament medial restraint to lateral sublimation. and Tibia! Tuberosity The articularis genus, asmall and variable muscle, is sometimes blended with the vastus intermedius The patellar ligament is a strong, thick band, which is (Williams & Warwick, 1980). It arises from the distal really a continuation of the quadriceps tendon and is femur and inserts into the synovial capsule and walls often called the patellar tendon. It originates at the in- of the suprapatellar pouch. The muscle functions to ferior pole of the patella and inserts onto the tibia1 tu- retract the suprapatellar pouch superiorly during ex- berosity (Williams& Warwick, 1980).The superior part tension of the leg. Dysfunction of the articularis ge- of the ligament overlies the infrapatellar fat pad, and nus has been attributed as one possible cause of the inferior part overlies the deep infrapatellar bursa. posttrauma patella baja (Mariani & Caruso, 1979). The central third of the patellar tendon is currently the

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