1986; 66:1246-1250.PHYS THER. T J Antich and Clive E BrewsterExercises During Knee RehabilitationModification of Quadriceps Femoris Muscle

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Modification of Quadriceps Femoris Muscle Exercises During Knee Rehabilitation

T. J. ANTICH and CLIVE E. BREWSTER

Rehabilitation of the quadriceps femoris muscle is the cornerstone of full recovery after inactivity, immobilization, or surgery of the knee. Muscle strengthening programs often are interrupted by patients' complaints of pain experienced during exercise, which frequently prolong the patients' convalescence period. Specific modifications of standard quadriceps femoris muscle exercises often allow completely pain-free exercise, thus providing a faster progression of treatment and a subsequently shorter rehabilitation period. The purposes of this article are to review briefly patellofemoral biomechanics as it relates to quadriceps muscle rehabilitation and to summarize several modifications that in our clinical experi-ence repeatedly have reduced pain during exercise.

Key Words: Exercise therapy, Knee joint, Physical therapy.

Rehabilitation techniques that accel-erate recovery time after knee injuries or surgery for knee injuries are an inte-gral part of the treatment process. Atro-phy and hypotonia of the quadriceps femoris muscle group frequently pro-long the patient's recovery after inactiv-ity, immobilization, and surgery of the knee. Complaints of pain and swelling also often hinder the physical therapist's efforts to restore the patient's normal muscle bulk and tone.

Through the phenomenon known as "reflex inhibition," muscular force out-put and electromyographic activity gen-erated with maximal voluntary contrac-tion are decreased in the presence of pain or effusion.1 The experimental studies of deAndrade and associates us-ing surface-electrode EMGs demon-strated reduced motor unit firing during a maximal voluntary contraction of muscles surrounding a joint experimen-tally distended with a saline solution.2 After the aspiration of excess fluid, EMG activity with maximal voluntary contraction increased to the preinfiltra-tion levels.

Clinically, we also have observed the reduced ability of patients to perform quadriceps femoris muscle exercises while experiencing either knee-joint or patellofemoral-joint (PFJ) pain. Al-though the effects of a local anesthetic on quadriceps femoris muscle inhibition after a meniscectomy have been meas-ured,1 the definitive study of the effects of using the infiltration of a local anes-thetic to decrease PFJ pain and simul-taneously measuring muscular output or EMG activity has not been conducted to date.

Our clinical experiences have brought us in contact with many patients who have pain while performing quadriceps sets (QSs) and short arc quadriceps fem-oris muscle (SAQ) exercises. The pur-pose of this article is to review some techniques that we have found to be effective for decreasing or eliminating knee pain in patients performing quad-riceps femoris exercises. Theoretical ex-planations will be offered to elucidate some of the mechanical changes that we believe occur In the knee when the standard exercises are modified. This article is based on the premise that pain-free quadriceps femoris strengthening will be more productive and beneficial to the rehabilitation programs of all pa-tients than if pain is present with the individual exercises.

One exercise commonly used to strengthen the anterior thigh muscula-ture is the QS. This exercise is performed by isometrically contracting the quadri-ceps femoris muscle with the knee in a position of full extension. This exercise,

usually performed for a 6- to 10-second duration, has been shown to produce greater EMG activity than either straight-leg or active knee-extension ex-ercises.3

We believe that isotonic quadriceps femoris muscle exercises, performed either through the full active range of motion or in terminal extension, SAQ, are superior to straight leg raising be-cause active movement at the knee joint places the greatest load on the quadri-ceps femoris muscles. In our clinic, the weight is raised concentrically and maintained for 10 seconds before low-ering through the range eccentrically, hence the term static weight lift (Fig. 1). Isometrically holding for 10 seconds may make the patient concentrate more intensely on controlling knee extension and ensures that he raises the weight through the maximum available exten-sion where the knee-joint kinematics place the quadriceps femoris at a bio-mechanical disadvantage.

Before reviewing the specific modifi-cations used for the QS and static-weight-lift exercises, we will discuss a few general principles of both static and dynamic tibiofemoral and patello-femoral biomechanics.

KNEE BIOMECHANICS

Patellofemoral Contact Points at Varying Degrees of Knee Flexion

Dye contact and photographic studies have evaluated the contact areas be-tween the patella and the femur as the knee flexes and extends.4 At 20 degrees

Mr. Antich is Chief Physical Therapist, Sports Medicine Inc, 233 E Lancaster Ave, Ardmore, PA 19003 (USA). At the time of this study, he was Staff Physical Therapist, Kerlan-Jobe Orthopaedic Clinic, 501 E Hardy St, Suite 200, Inglewood, CA 90301, and Research Physical Therapist, Biome-chanics Laboratory, Centihela Hospital Medical Center, 555 E Hardy St, Inglewood, CA 90307.

Mr. Brewster is Director of Physical Therapy, Kerlan-Jobe Orthopaedic Clinic.

This article was submitted April 29, 1985; was with the authors for revision four weeks; and was accepted November 25, 1985.

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PRACTICE

Fig. 1. Terminal extension static weight lift performed with weight boot for quadriceps femoris muscle strengthening.

Fig. 2. Patellofemoral contact areas at varying degrees of knee flexion. (Adapted from Goodfellow et al.4)

Fig. 3. Ankle dorsiflexion combined with quadriceps femoris muscle setting to de-crease patellofemoral joint pain.

cf flexion, only the inferior pole of the patella is in contact with the femur. The point of contact moves proximally on the patella as the knee flexes to 45 de-grees and then to 90 degrees (Fig. 2). At full flexion, only the odd facet and the lateral facet approximate the medial and lateral femoral condyles, respectively. Patients with localized degenerative changes in one part of the retropatellar articular cartilage may experience pain in one position but not at another, de-pending on whether the compression forces on the damaged area are in-creased or decreased.

Osseous Stability of the Patella in the Intercondylar Groove

The more stable configuration of the patella in the femoral intercondylar groove occurs with increasing angles of knee flexion, and in the last 15 to 20 degrees of extension the patella rides proximally out of the groove. Medial-lateral stability must depend on the static tautness of the retinacula and the dynamic control of the vastus medialis oblique (VMO) muscle in the absence of osseous congruence. This normal PFJ

stability will be disrupted in patients with patella alta, hypotrophic femoral intercondylar grooves, patellar subluxa-tion, and hyperelastic connective tis-sues.

Terminal Extension

Tibial external rotation occurs at the end of terminal extension ROM in a foot-free position. If active hyperexten-sion is attainable, if the patient has a laterally located tibial tubercle, or if an abnormally excessive valgus malalign-ment of the knee exists, excessive lateral excursion of the patella may result at the end of the ROM.

Role of the VMO in Normal Dynamic Patellar Biomechanics

Oblique fibers of the VMO muscle inserting at 55 degrees to the long axis of the femur primarily are responsible for maintaining proper patellar track-ing.5 Lieb and Perry demonstrated that this tracking is the muscle fibers' only function because structurally the fibers are not in the proper position to act as a synergist to the rest of the muscle group functioning as a knee extensor.6 Clinically, we often have observed PFJ pain to be related to VMO muscle hy-potonia. Experimental infiltration of the knee joint with a saline solution dem-onstrated greater inhibition of muscle activity in the VMO than in the rectus femoris or vastus lateralis.7

Anterior-Posterior Tibial Displacement

The cruciate ligaments are the pri-mary static restraints against tibio-femoral sagittal shear forces. The role of the quadriceps femoris and hamstring muscles as the dynamic synergist to the posterior cruciate ligament (PCL) and anterior cruciate ligament (ACL), re-spectively, has been stressed in rehabili-tation by Brewster et al8 and by other physical therapists (K. R. Glick, per-sonal communication, July 1983). Al-though injuries to the ACL outnumber those to its posterior counterpart by a ratio of 10:1, quadriceps femoris muscle contraction in the ACL-deficient or ACL-reconstructed knee may result in excessive anterior tibial displacement with stress being dissipated to other sec-ondary restraints or to the new graft, either of which may result in pain.

MODIFICATIONS

Ankle Dorsiflexion The most successful modification of

the QS exercise for decreasing PFJ pain is active dorsiflexion (DF) of the ankle before contraction of the quadriceps femoris muscles (Fig. 3). Many acade-micians teach ankle DF as a standard part of the exercise to generate an in-creased contraction force. This result, however, was not substantiated by our

Volume 66 / Number 8, August 1986 1247

Fig. 4. Avoiding full extension with a small wedge.

Fig. 5. Decreasing the Q angle by inverting and dorsiflexing the ankle.

Fig. 6. Isometric hip adduction before quad-riceps femoris muscle exercises.

Fig. 7. Assessment of medial manual track-ing; a, superficial tissues are pushed laterally and b, the deeper retinaculum is pulled me-dially.

own research in which we compared EMG outputs recorded using indwelling wire electrodes (D. R. Moynes et al, unpublished data, 1982). We believe that active ankle DF actually may in-hibit contraction of the quadriceps fem-oris muscle because it is part of the flexor withdrawal reflex with associated hamstring muscle facilitation and quad-riceps femoris muscle inhibition. This hypothesis may be supported by our clinical observations that pain persists when the quadriceps femoris muscles are contracted with a relaxed ankle but is relieved when active DF (with a re-duction of quadriceps femoris strength and, therefore, of PFJ pain) precedes the contraction. The decreased pain may be caused by the decreased force of the

quadriceps femoris contraction. Another possible reason that pain

may be reduced with ankle DF is the resultant passive stretch on the antago-nistic calf musculature. The position of the knee in full extension exerts maxi-mal stretch on the gastrocnemius mus-cle because it is a two-joint muscle. Crossing the posterior aspect of the knee joint, the gastrocnemius muscle may flex the knee passively a slight amount because the ankle is in DF, thus elimi-nating pain at full extension.

Use of Small Wedge

Patients who have either knee-joint effusion or pain with the standard QS position at full extension may benefit

from having the knee positioned in vary-ing degrees of flexion. Figure 4 illus-trates the use of a small wedge under the knee to reduce PFJ pain. This mod-ification may benefit patients with in-flammation of either the plica or the infrapatellar fat pads because a QS in the position of full extension often ag-gravates those conditions. Those pa-tients with patellar tracking problems may benefit from the slightly improved bony congruity of the patella in the fem-oral groove when exercising isometri-cally in a few degrees of flexion.

Patients with a rupture of the ACL or with post-ACL reconstruction always should use at least a small wedge when performing QS exercises. Maintaining the knee in slight flexion prevents hy-perextension if the heel is kept on the mat and also decreases stress on the posterolateral bundle of the ACL,9 the secondary restraints, and the ligament graft.

Ankle Dorsiflexion with Inversion

Actively inverting the foot in combi-nation with ankle DF may benefit pa-tients with patellar malalignment when DF alone is ineffective. Dorsiflexing the ankle locks the talocrural joint, and the subsequent inversion prevents excessive external rotation of the tibia, moving the tubercle slightly more medially (Fig. 5). By decreasing the lateral shear forces exerted on the patella and the medial retinaculum, parapatellar pain may be reduced effectively.10

Isometric Hip Adduction

Patients with PFJ symptoms may achieve pain relief by performing iso-metric hip adduction exercises before performing knee-extension exercises (Fig. 6). Although isometrically adduc-ing the hips (2 sets of 10 repetitions, each of 10 seconds' duration) does not elicit a VMO muscle contraction auto-matically, performing hip adduction ex-ercises before knee-extension exercises has been observed to result in decreased pain (D. R. Moynes et al, unpublished data, 1982). Because the VMO muscle originates, in part, from the fascia over-lying the adductor magnus muscle,11 ex-ercising this larger muscle first may gen-erate tension within it, thereby placing the VMO muscle at a better mechanical advantage and resulting in decreased lat-eral shearing.

1248 PHYSICAL THERAPY

PRACTICE

Fig. 8. Electromuscular stimulation of the vastus medialis oblique muscle in conjunction with isometric exercises.

Electromuscular Stimulation

Electromuscular stimulation is a val-uable adjunct to quadriceps femoris muscle exercises for decreasing peripa-tellar pain resulting from selective weak-ness of the VMO muscle. An evaluative technique called medial manual track-ing can identify those patients who may achieve pain relief with the use of elec-tromuscular stimulation. The therapist first places his hand on the medial aspect of the knee joint, dropping his thumb just medial and superior to the patella (directly overlying the VMO muscle). Pushing the superficial skin and subcu-taneous layers laterally (Fig. 7a), he then exerts deeper pressure and, feeling the underlying retinaculum, pulls back me-dially (Fig. 7b). After the patient has contracted his quadriceps femoris, the therapist then should then evaluate the patient's perceived level of pain. For patients with a dystrophic VMO muscle or stretched medial stabilizers, electro-muscular stimulation actually takes the place of the absent or reduced VMO muscle contraction. If pain is relieved substantially by medial manual track-ing, the use of electromuscular stimula-tion on the VMO muscle is likely to be successful.

When administering electromuscular stimulation for VMO muscle strength-ening, the best results may be obtained by using electrodes of different sizes. The smaller electrode should be placed over the motor point of the VMO mus-cle, resulting in a higher current density under this pad (Fig. 8). The duty cycle may be adjusted in most units to corre-spond to the length of the contraction

Fig. 9. Starting with the knee in more flex-ion allows the vastus medialis oblique muscle time to contract earlier and prevent lateral tracking problems.

desired. Active quadriceps femoris mus-cle exercises then are performed, aug-mented by the electromuscular stimu-lation.

Static Weight Lifts

Standard static weight lifts are per-formed using ankle cuff weights or a weight boot over a roll about 6 in in diameter, thus using a ROM of about 35 degrees to full extension. All of the previously discussed modifications (an-kle DF, ankle DF with inversion, wedge, electromuscular stimulation) may be used with this form of isotonic muscle strengthening.

Pain may be eliminated with static weight lifts if the painful location within the arc of motion can be determined. Pain may be experienced during either concentric or eccentric movements, or both; at the beginning of ROM; or at the end of ROM. In 151 cases of PFJ symptoms studied in our clinic, more knees were symptomatic of pain with concentric contractions (11%) than with eccentric contractions (5%), although 75% exhibited no pain with active knee extension through a 90-degree arc.12

Starting in More Flexion

Clinically, more patients have pain at full extension than at other positions in the ROM. This position may be modi-fied by using larger rolls to increase the height of the fulcrum (Fig. 9). Beginning with the knee in a more flexed position affords the patient a position of better PFJ osseous stability because the patella is seated better in the intercondylar groove. In patients with "quadriceps re-versal"13 or delayed firing of the VMO muscle during active ROM, the greater range allows a longer time for activation of this dynamic medial stabilizer to re-duce lateral tracking problems.

Ice Before Exercise

If none of the aforementioned modi-fications either substantially reduce dis-comfort with exercise or completely eliminate pain, the knee may be treated with ice for 10 minutes before exercise is performed. Depending on the level of pain after cryotherapy, the therapist must use clinical judgment and experi-ence to determine whether exercise per-formed with pain will aggravate the pa-tient's condition.

Hamstring Cocontraction

Patients with increased anterior ex-cursion of the tibia on the femur (because of ACL insufficiency) during isotonic quadriceps femoris muscle ex-ercises should be instructed to contract the hamstring muscles for one second before lifting the leg. Coactivation of the knee flexor muscles during knee-exten-sion exercises decreases the anterior shear of the tibia and provides for more normal biomechanical functioning be-cause of better maintenance of the axis of rotation.

CONCLUSIONS

Quadriceps femoris muscle strength-ening forms the foundation for both nonsurgical and postoperative rehabili-tation programs. Goldfuss et al reported that passive medial and lateral knee-joint opening to externally applied force was reduced in actively contracted quadriceps femoris muscles when com-pared with that instability measured in a relaxed state.14

Optimal quadriceps femoris muscle contractions are achieved best in the absence of pain. We have reviewed our methods of reducing pain in patients performing quadriceps femoris muscle exercises and hope that some of the techniques discussed may not only im-prove the quality of patient care, but also stimulate further related research.

Acknowledgments. We acknowl-edge the assistance of the following members of the Kerlan-Jobe Ortho-paedic Clinic Physical Therapy Re-search Committee in the preparation of this manuscript: Celeste Criswell Ran-dall, MS, RPT; Roxie A. Westbrook, RPT; and Matthew C. Morrissey, MA, RPT.

Volume 66 / Number 8, August 1986 1249

REFERENCES 1. Stokes M, Young A: Investigations of quadri-

ceps inhibition: Implication for clinical practice. Physiotherapy 70:425-428,1984

2. deAndrade JR, Grant C, Dixon A St. J: Joint distension and reflex muscle inhibition in the knees. J Bone Joint Surg [Am] 47:313-322, 1965

3. Pocock GS: Electromyographic study of the quadriceps during resistive exercise. J Amer Phys Ther Assoc 43:427-434,1963

4. Goodfellow JW, Hungerford DS, Zindel M: Pa-tello-femoral joint mechanics and pathology: 1. Functional anatomy of the patello-femoral joint. J Bone Joint Surg [Br] 58:287-290,1976

5. Lieb FJ, Perry J: Quadriceps function: An ana-tomical and mechanical study using amputated limbs. J Bone Joint Surg [Am] 50:1535-1548, 1968

6. Lieb FJ, Perry J: Quadriceps function: An elec-tromyographic study under isometric condi-tions. J Bone Joint Surg [Am] 53:749-758, 1971

7. Spencer JD, Hayes KC, Alexander lJ: Knee joint effusion and quadriceps reflex inhibition in man. Arch Phys Med Rehabil 65:171-177, 1984

8. Brewster CE, Moynes DR, Jobe FW: Rehabili-tation for anterior cruciate reconstruction. Jour-nal of Orthopaedic and Sports Physical Ther-apy 5:121-126,1983

9. Paulos L, Noyes FR, Grood E, et al: Knee rehabilitation after anterior cruciate ligament reconstruction and repair. Am J Sports Med 9:140-149, 1981

10. Olerud C, Berg P: The variation of the Q angle with different positions of the foot. Clin Orthop 191:162-165,1984

11. Bose K, Kanagasuntheram R: Vastus medialis oblique: An anatomic and physiologic study. Orthopedics 3:880-889,1980

12. Antich TJ, Randall CC, Westbrook RA, et al: Evaluation of knee extensor -mechanism dis-orders: Clinical presentation of 112 patients. Journal of Orthopaedic and Sports Physical Therapy, to be published

13. Williams JGP, Street M: Sequential faradism in quadriceps rehabilitation. Physiotherapy 62:252-254,1976

14. Goldfuss AJ, Morehouse CA, LeVeau BF: Ef-fect of muscular tension on knee stability. Med Sci Sports 5:267-271,1973

Commentary

The opportunity to write a commen-tary may be viewed as being asked for a second opinion. A second opinion may agree with or disagree with the initial interpretation. This commentary is a discussion of only those concepts with which I disagree that were presented in the article.

The term static weight lift is mislead-ing. A more accurate term for the exer-cise might be dynamic-static-dynamic weight lift. Because a subject performs an isometric contraction and concen-trates intensely does not ensure that he will lift the weight through the maxi-mum available range of motion. The ability to raise the weight through the available ROM also depends on whether enough innervated and cross-sectional areas of muscle tissue exists.

The authors suggest that active dorsi-flexion and inversion of the foot prevent excessive tibial external rotation, result-ing in a more medial displacement of the tubercle (tuberosity) and providing a beneficial effect on the valgus move-ment of the patella during knee exten-sion. Although the authors cite the re-search of Olerud and Berg1 to support this concept, they do not mention that Olerud and Berg's research was con-ducted in a closed kinetic chain with the subject's foot on the ground. The mod-ified quadriceps femoris muscle exercise

program presented in the article appears to use an open-kinetic-chain type of ac-tivity. The biomechanics of tibial rota-tion and subtalar motion are distinctly different in an open kinetic chain as compared with a closed kinetic chain.2,3 If the knee is not in a closed pack posi-tion, then the motion of inversion of the foot may prevent excessive tibial exter-nal rotation. In an open kinetic chain, however, when the tibia is in the last few degrees of extension or the first few de-grees of flexion, the tibial rotation is a function of the arthrokinematics of the knee joint and not of the position of the foot.4,5 The medial rotation of the tibial tubercle observed with inversion of the foot in an open kinetic chain probably is a function of femoral internal rotation that may result if the subject is in-structed to rotate his foot inwardly.

The authors do not mention the rea-sons for exercising the knee in a closed kinetic chain in their discussion of their modifications of quadriceps femoris muscle exercises. Hungerford and Len-nox have reported a biomechanical analysis demonstrating less patellofem-oral contact stress from 30 to 60 degrees of knee flexion in a closed kinetic chain versus an open kinetic chain.6 As the knee flexes, patellofemoral-joint-reac-tion (PFJR) forces increase, but so does the patellofemoral contact area, which

aids in the distribution of PFJR forces so that patellofemoral stress is de-creased.7

Preliminary data also are available supporting the use of closed-kinetic-chain exercises for patients with anterior cruciate ligament (ACL) injuries.7 Using an in vivo strain gage, Henning et al demonstrated with values normalized to the individual that one of the activities that caused the greatest strain to be placed on the ACL was knee-extension exercises using a 20-lb weight boot in the range of full extension to 22 degrees of flexion.7 The ACL was subjected to much less strain during a half-squat ex-ercise.

Perhaps, quadriceps femoris muscle exercises should be modified to include more closed-kinetic-chain types of activ-ities such as the lateral or anterior step-up exercises.8,9 In my experience, if the patient is allowed to pronate during the lateral step-up exercise, the valgus knee angle is increased, which is believed to be detrimental to patients with patello-femoral disorders.10

In an open kinetic chain, patello-femoral contact stress is greatest from 55 degrees of flexion to full extension.6 The modification of the static weight lift proposed by the authors to be performed from 35 degrees of flexion to full exten-sion in an open kinetic chain, therefore, is in the ROM that creates the greatest, and possibly harmful, patellofemoral contact stress. The authors suggest that the static weight lift may be initiated in greater degrees of flexion because it af-fords better patellofemoral osseous sta-bility. The study of Hungerford and Lennox provides an alternative ration-ale for using greater degrees of flexion during open-kinetic-chain knee exten-sion in that patellofemoral contact stress is less from 55 to 75 degrees of flexion.6 With open-kinetic-chain, knee-exten-sion resistive exercise, therefore, the greater the degree of knee flexion, the less the patellofemoral contact stress.

In a qualified statement, the authors suggest that electromuscular stimulation is a valuable adjunct to quadriceps fem-oris muscle exercises for strengthening the vastus medialis oblique muscle. Al-though the validity of this statement cannot be proven because measuring in vivo the tension-generating capability of an individual quadriceps femoris mus-cle is impossible, I will assume that the vastus medialis oblique muscle can be strengthened selectively with knee-ex-

1250 PHYSICAL THERAPY