INJURY CLINIC

Sports Medicine 12 (5): 338-346, 1991 0112-1642/91/0011-0338/$04.50/0 © Adis International Limited. All rights reserved.

SP0156a

Rehabilitation Concerns Following Anterior Cruciate Ligament Reconstruction Philip A. Frndak and Carl C. Berasi Doctors Hospital, Columbus, Ohio, USA

Contents

338 339 340 342 343 343 344

Summary

Summary I. Early Motion 2. Protection of the Biological ACL Graft 3. Strength Recovery 4. Neuromuscular Re-Education 5. Knee Braces 6. Conclusion

Rehabilitation following anterior cruciate ligament reconstruction is a subject of controversy in the orthopaedic and rehabilitation literature. With an increasing number of these operations currently being performed and with the advent of arthroscopically assisted ACL reconstruction over the past several years, particular rehabilitation needs and problems have been identified in association with these patients.

Various authors have stressed one or a combination of a few basic themes which outline the basic rehabilitation concerns following ACL reconstruction. The most fundamental concern is the need to initiate motion very soon after surgery. Prolonged postoperative immobilisation is known to cause serious complications after ACL reconstruction which can be avoided by early motion.

Positions or activities which may apply excessive stress to a newly reconstructed ACL must also be considered. The amount of protection required by the graft will vary depending upon the type of graft used and the quality of fixation obtained intraoperatively. Most authors agree that nonweightbearing, active resistive quadriceps exercises should be avoided for an extended period, while closed chain exercises may be initiated much earlier_

Strength recovery is obviously important for the quadriceps postoperatively, but maximal strength returns of all of the muscles about the knee must be pursued. Hamstring strength is of particular concern as this may provide an active support to the reconstructed ACL.

Sensory loss in the knee after ACL disruption should also be addressed during rehabilitation, prior to a patient's return to full athletic activity. Progressive neuromuscular re-education exer­cises which rely on sensory input from intact pericapsular structures are encouraged.

A final concern is the role of bracing after ACL reconstruction. Rehabilitative braces are in common use postoperatively to limit the patient's knee motion to that dictated by the physician. The use of braces during heavy athletic activity following anterior cruciate ligament reconstruc­tion is less well supported by the literature. Although the physician may choose to prescribe such

Rehabilitation After ACL Reconstruction 339

a device, the role of a brace must be considered secondary in comparison to the need for a strong, agile lower extremity to protect the ACL graft.

In conclusion, the trends in rehabilitation following ACL reconstruction are increasingly fo­cused on maximising the rate of recovery and return to full function while achieving optimal results. To reach this goal, a thorough understanding of the rehabilitation approach is necessary. In addition, significant questions remain with respect to the amount of stress a newly recon­structed ACL is able to tolerate during the various phases of recovery.

The goal after anterior cruciate ligament recon­struction is a biomechanically normal knee with respect to motion, strength and stability. Current techniques in arthroscopic reconstruction restore passive stability assuming that the new ligament is well placed (Jackson & Jennings 1988; Melhorn et al. 1987; Penner et al. 1988), strong enough to withstand physiological stresses (Blackburn 1985; Graf & Uhr 1988; Noyes et al. 1984), and is per­mitted to heal in this position without disruption or displacement (Arms et al. 1984; Draganich et al. 1989; Graf & Uhr 1988; Grana & Muse 1988; Ku­rosaka et al. 1987; Maltry et al. 1989). Motion, strength and dynamic stability must be regained during postoperative rehabilitation.

Large studies documenting the long term bene­fits after ACL reconstruction utilising current tech­niques are not in abundance, but those published offer encouraging data (Boden et al. 1990; Sand­berg et al. 1988; Seto et al. 1988; Tibone & Antich 1988). The reconstructed knees appear to be stronger, more stable and better able to withstand the stresses of athletic performance than ACL-de­ficient knees (Clancy et al. 1982; Tibone & Antich 1988). Today, as in other areas of orthopaedics, emphasis is increasingly focused on maximising the rate of recovery and return to full function while achieving optimal results (Jackson & Jennings 1988).

Various themes arise repeatedly in the literature which address rehabilitation approaches after ACL reconstruction. These include avoidance of the complications of prolonged immobilisation (An­derson & Lipscomb 1989; Graf & Uhr 1988; Hue­gel & Indelicato 1988; Jakson & Jennings 1988; Konh 1990; Noyes et al. 1984, 1987; Shelbourne & Nitz 1990; Sprague 1987; Wilcox et al. 1987),

avoidance of positions or actIVItIes which may compromise the integrity of a freshly placed graft (Anderson & Lipscomb 1989; Arms et al. 1984; Blackburn 1985; Delitto et al. 1988b; Graf & Uhr 1988; Grana & Muse 1988; Huegel & Indelicato 1988; Kain et al. 1988; Kurosaka et al. 1987; Noyes et al. 1984; Paulos et al. 1981; Steadman 1983; Wil­cox et al. 1987), the need to regain muscular strength after surgery (Anderson & Lipscomb 1989; Baratta et al. 1988; Coughlin et al. 1987; Delitto et al. 1988b; Draganich et al. 1989; Elmqvist et al. 1989; Huegel & Indelicato 1988; Paulos et al. 1981; Sisk et al. 1987; Steadman 1983; Wilcox et al. 1987), the importance of neuromuscular re-education to maximise coordination and fine kinaesthetic con­trol (Anderson & Lipscomb 1989; Baratta et al. 1988; Blackburn 1985; Draganich et al. 1989; Ger­ber et al. 1985; Huegel & Indelicato 1988; Paulos et al. 1981; Seto et al. 1988; Solomonow et al. 1987; Steadman 1983) and the role of bracing after sur­gery (American Academy of Orthopaedic Surgeons 1984; Bessette & Hunter 1990; Shelbourne & Nitz 1990). Presented below is a review of these con­cerns based on the current literature.

1. Early Motion

Less than 10 years ago at least 6 weeks of strict immobilisation was the norm after ACL recon­struction (Anderson & Lipscomb 1989; Arms et al. 1984; Clancy et al. 1982; Huegel & Indelicato 1988; Malone et al. 1980; Paulos et al. 1981; Steadman 1983). Complications associated with this ap­proach included intra-articular adhesions, infra­patellar adhesions, patellofemoral crepitation, joint stiffness and profound quadriceps atrophy (Ander­son & Lipscomb 1989; Graf & Uhr 1988; Sprague

340

1987; Wilcox et al. 1987}. Other complications as­sociated with immobility are also well described and include declines in the biomedical properties of bone, ligament and cartilage (Anderson & Lip­scomb 1989; Noyes et al. 1977; Salter et al. 1980).

In the mid 1980s the literature began to reflect a thrust to move the freshly operated knee more quickly in an effort to avoid these complications (Noyes et al. 1984, 1987). The literature however, is not in complete agreement with respect to how soon the knee should be moved, or with what re­strictions after an intra-articular reconstruction. Continuous passive motion has been utilised im­mediately after surgery by many (Anderson & Lip­scomb 1989; Graf & Uhr 1988; Shelbourne & Nitz 1990), while others prefer early passive motion fol­lowing a brief period of immobilisation, typically lasting 2 weeks or less (Huegel & Indelicato 1988).

Frequently, motion is permitted very early al­though with restrictions in range. Anderson and Lipscomb (1989), for example, examined various protocols of rehabilitation following ACL recon­struction, including one which provided 2 weeks ofimmobilisation followed by limited passive mo­tion from 35 to 70°. Full extension was delayed for 3 months in this protocol. On the other hand, Graf and Uhr (1988), Wilcox et al. (1987) and Shel­bourne and Nitz (1990) encourage immediate full range of motion.

The rationale for limiting extension and initi­ating only passive motion in the early postopera­tive phase (Huegel & Indelicato 1988) is discussed in the following section.

2. Protection of the Biological ACL Graft

Investigation of the biomechanics of the knee has identified numerous positions and activities which induce a traction stress on the intact anterior cruciate ligament (Arms et al. 1984; Gerber et al. 1985; Henning et al. 1985; Jurst & Otis 1985; Kain et al. 1988; Maltry et al. 1989; Noyes et al. 1987). Examination of passive positioning has revealed that the maximally flexed and extended position of the knee cause increased stress on an intact ACL, in comparison to mid-range positions (Gerber et

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al.1985). For this reason some authors encourage avoidance of these postures in the early phases after ACL reconstruction.

Active, isolated quadriceps contraction in a nonweightbearing position is also associated with a potentially undesirable anterior drawer force on the proximal tibia, particularly from 45" to full ex­tension (Arms et al. 1984; Henning et al. 1985; Huegel & Indelicato 1988). The vector associated with this force increases steadily until full exten­tion is achieved. This stress can be neutralised by the use of simultaneous isometric co-contractions of the hamstrings with the quadriceps (Anderson & Lipscomb 1989; Arms et al. 1984; Blackburn 1985; Nitz & Dobner 1987) or by disallowing ex­tension beyond 60° when performing isolated quadriceps contractions (Anderson & Lipscomb 1989; Arms et al. 1984; Jurst & Otis 1985; Maltry et al. 1989). Isometric co-contraction of the hamstrings with the quadriceps adds a posterior drawer force to the proximal tibia to neutralise the anteriorly directed stress induced by the quadri­ceps. This technique is believed to protect the ACL from excessive traction stress except in full exten­sion. Alternatively, by positioning the knee in 60° of flexion during the exercise, the vectors associ­ated with isolated quadriceps contractions are al­tered to minimise any force towards anterior sub­luxation. Utilising techniques such as these allows the initiation of safe quadriceps strengthening ex­ercises much earlier than is otherwise possible after ACL reconstruction. Typically, routine active re­sistive quadriceps strengthening exercises are de­layed for several months following ACL recon­struction (Huegel & Indelicato 1988; Wilcox et al. 1987), and as long as a year in one report (Henning et al. 1985). The exercises discussed above are be­gun within the first 2 weeks after surgery (Delitto et al. 1988a,b).

Other activities, such as weightbearing exercises and cycling, have been examined with respect to a reference stress manoeuvre. Such activities provide another means of safely strengthening the lower ex­tremity during the early postoperative phases. Lower extremity weightbearing, in a position such as a I-leg half-squat, requires simultaneous quad-

Rehabilitation After ACL Reconstruction

riceps and hamstrings contractions (Tiberio & Gray 1989). The quadriceps group functions concentri­cally to extend the knee, isometrically, or eccen­trically to limit further knee flexion. During this activity the hamstrings function concurrently as strong hip extensors. This simultaneous contrac­tion of the hamstrings with the quadriceps, along with axial compression of the joint surfaces, effec­tively limits anterior translation of the proximal tibia on the femur which would etherwise occur with an isolated, nonweightbearing quadriceps contraction of equal intensity (Fanton 1987; Shel­bourne & Nitz 1990). Biomechanical principles such as these can be applied to safely accelerate the re­habilitation approach after ACL reconstruction.

To provide an illustration, Henning et al. (19S5) looked at ACL stresses compared to a reference 80lb Lachman manoeuvre. Cycling produced 7% as much elongation as an 80lb Lachman test. A I-leg half-squat produced 21 % and quadriceps contrac­tions against a 20lb weight boot at 45" of knee flex­ion produced 50% as much elongation as the ref­erence manoeuvre. Quadriceps contractions near the terminal ranges of knee extension produced elongation forces of 87 to 121 % of their reference 80lb Lachman manoeuvre. They believe that the proper order of a rehabilitation programme should be crutch walking, cycling, walking, slow running and faster running.

The surgeon's choice of an ACL replacement and the type of fixation utilised are also major factors in considering the amount of protection necessary for a freshly placed ACL graft (Indelicato et al. 1989; Kurosaka et al. 1987; Noyes et al. 1984). The type of healing that the graft is expected to undergo, the specific strength of the graft chosen and the quality of fixation obtained at the time of surgery should all be considered in deciding how much stress on the graft to permit during the healing phases. Al­though insufficient research has been done in this area, some facts have been established.

During the early stages of healing, failure of an ACL graft typically occurs at the fixation site (Noyes et al. 1984). The commonly utilised middle one­third patellar tendon graft is believed to become fixed in position via bony and or fibrous healing

341

within 6 to 8 weeks of surgery (Huegel & Indelicato 1988), but some reports have stated that 3 to 4 months may be necessary for the reconstructed graft to have solid anchorage at the fixation site (Noyes et al. 1984).

Revascularisation and remodelling of the graft is a longer process which may be just reaching its peak 6 months following surgery (Graf & Uhr 1988; Huegel & Indelicato 1988). During this time the integrity of a graft is particularly compromised. The mechanical strength of the revascularised and re­modeled patellar tendon graft is less than 50% of the original ACL 3 to 4 months after surgery (Cur­rier & Mann 1983; Noyes et al. 1984). On the other hand, this type of biological graft is considered the strongest of the commonly utilised ACL substi­tutes. A 14mm wide bone-patellar tendon-bone autograft measures 168% as strong as a healthy an­terior cruciate ligament during in vitro testing (Ku­rosaka et al. 1987; Noyes et al. 1984). When com­pared to other tissues about the knee, this graft has been found to have the greatest strength within its substance (Noyes et al. 1984) as well as the greatest pullout strength when secured through interference fit with a large diameter cancellous screw (Kuro­saka et al. 1987). The significance of this infor­mation is that each type of anterior cruciate liga­ment graft will have different inherent limitations in its ability to withstand stress. Depending on the specific graft which has been used to replace the normal ACL, the rehabilitation approach may re­quire alteration to provide either increased protec­tion or freedom of activity. Additionally, it is es­sential to understand the biological limitations of the healing process when planning a progressive re­habilitation programme. Although it may be tempting to initiate more advanced activities as soon as the patient 'feels ready', the state of healing of the graft should always be of primary consid­eration. Maximally stressful activities should be avoided until the substitute ACL is believed to be strong enough to withstand heavy forces.

In summary, it appears that certain activities may be placed on a rough scale with respect to the amount of traction they tend to impart to the ACL. At one end of the spectrum the least amount of

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stress on the ligament" would be strict immobilis­ation in a position of 30 to 40° of flexion. Rela­tively minimal stress on the ligament occurs with passive motions from 60 to 30°. Full passive range of motion, cycling and crutch walking with partial weightbearing may be the next level of activity, fol­lowed by full weightbearing. Lower extremity strengthening through the use of weightbearing ex­ercises should follow, while isolated nonweight­bearing quadriceps contractions near the final de­grees of extension should be near the top end of this scale. The maximum stress studied by Hen­ning et al. (1985) and Arms et al. (1984) was ap­parently nonweightbearing, actively resisted knee joint extension to 0°. Although not specifically mentioned in these studies, all of the above would be much less stressful than the potential forces act­ing on the knee during certain athletic activities.

Important information has been accumulated regarding the ways in which various biological ACL replacements compare with each other in the la­boratory setting, as well as how much stress vari­ous activities induce within the normal ACL in comparison to one another. However, the exact amount of stress that is applied in vivo is unknown and exactly how much stress each graft can safely tolerate during postoperative healing remains in question.

3. Strength Recovery

Another theme frequently arising in the litera­ture is the need for strength recovery after ACL reconstruction (Anderson & Lipscomb 1989; Bar­atta et al. 1988; Draganich et al. 1989; Elmqvist et al. 1989; Graf & Uhr 1988; Kain et al. 1988; Seto et al. 1988; Solomonow et al. 1987; Tibone & An­tich 1988). Some of the issues in this topic have already been discussed above, but it is of import­ance to note that profound quadriceps atrophy oc­curs in association with an ACL tear (Huegel & Indelicato 1988). Most reports have failed to show complete normalisation of quadriceps strength in these patients when compared to their nonopera­tive side, in spite of postoperative assessments long after the index surgery (Elmqvist et al. 1989; Ti-

Sports Medicine 12 (5) 1991

bone & Antich 1988). Research has explored the types of quadriceps muscle fibres which could atro­phy disproportionately in comparison to others in an effort to identify the rates of speed at which a patient should exercise preferentially in the reha­bilitation phase. Histological studies have, how­ever, shown a uniform reduction in type I and type II muscle fibres, indicating that strengthening at every speed of contraction is equally important (Gerber et al. 1985).

The role of the hamstring musculature in the strength needs of this patient group is controversial (Antich & Brewster 1988; Baratta et al 1988; Bar­rack et al. 1989; Draganich et al. 1989; Paulos et al. 1981; Seto et al. 1988; Solomonow et al. 1987). The quadriceps are known to atrophy to a much greater extent than the hamstrings and for this rea­son some authors have encouraged emphasis on strengthening the knee extensors preferentially (Huegel & Indelicato 1988). Others have docu­mented the role of the hamstrings as a dynamic stabiliser of the knee (Antich & Brewster 1988; Baratta et al. 1988; Solomonow et al. 1987). Reflex arcs from the intact ACL and the joint capsule have been identified which support the likelihood that the hamstrings normally function to prevent over­load of the ACL (Solomonow et al. 1987). For this reason some authors have encouraged supernor­mal strength goals for the hamstring muscles in an effort to protect the reconstructed ACL and im­prove the ability of the patient to withstand the severe stresses placed on the ligament during ath­letic competition (Barrack et al. 1989; Tibone et al. 1986). Giove et al. (1983) have documented that higher levels of sports participation are found in ACL-deficient patients whose hamstring strength is equal to or more than their quadriceps strength. In these individuals the quadriceps strength was im­proved to near normal and the hamstrings to a higher than normal level when compared to their unaffected side.

Electrical muscle stimulation (EMS) is a sub­topic in the strengthening theme discussed in the literature (Currier & Mann 1983; Delitto et al. 1988a,b; Kain et al. 1988; Nitz & Dobner 1987; Selkowitz 1985; Sisk et al. 1987; Soo et al. 1988).

Rehabilitation After ACL Reconstruction

The primary goal in the use of EMS is the min­imisation of postoperative atrophy. Numerous ar­ticles have addressed this technique with some­what conflicting results. Delitto et al. (l988a,b), Nitz & Dobner (1987) and others have described sig­nificant clinical benefits from the use of EMS in the thigh musculature of patients with an injured, immobilised lower extremity. The benefits re­ported include decreased strength loss in the early postoperative phase, more rapid gains in range of motion, and increased overall rate of return to ath­letic activity. Other authors have reported less op­timistic results, stating that EMS was no more ef­fective than volitional exercise in maintaining thigh muscle strength in their studies (Selkowitz 1985; Sisk et al. 1987). Due to the numerous variables involved in the use of EMS it is very difficult to compare individual studies. Several factors may contribute to greater effectiveness in the use of electrical muscle stimulation. These include the ability of some to tolerate greater intensities of stimulation and therefore greater strengths of con­traction, the potential for direct electrical stimu­lation to overcome reflex muscle inhibition caused by painful periarticular structures and the possi­bility of a pain-blocking effect of electric stimula­tion (Delitto et al. 1988b; Kain et al. 1988; Sel­kowitz 1989). Studies which examined healthy subjects must be differentiated from those which dealt with postoperative patients. The use of EMS in healthy subjects is known to produce strength gains similar to those with volitional exercise (Sel­kowitz 1989). Direct electrical muscle stimulation may potentially be of greater benefit than voli­tional exercise alone to minimise strength losses in the immediate postoperative phase. This issue is controversial (Delitto et al. 1988a,b; Sisk et al. 1987).

4. Neuromuscular Re-Education

Another theme recurring in the literature of re­habilitation after ACL reconstruction is the need for neuromuscular re-education (Elmqvist et al. 1989; Huegel & Indelicato 1988). Preathletic train­ing exercises have been suggested for several years

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to help bridge the gap between routine postoper­ative rehabilitation and return to competitive ath­letic performance (Blackburn 1985; Huegel & In­delicato 1988; Paulos et al. 1981; Steadman 1983). Now it is known that the intact ACL had an im­portant sensory function in the normal knee (Bar­rack et al. 1989; Draganich et al. 1989; Gerber et al. 1985; Solomonow et al. 1987). Mechanorecep­tors have been demonstrated within the intact ACL which could be able to detect joint position as well as s.udden or slow joint position changes (Barrack et al. 1989; Draganich et al. 1989; Gerber et al. 1985). A decrease in overall neuromuscular drive may be responsible for the refractory strength and girth losses typically sustained by the quadriceps musculature after ACL disruption (Elmqvist et al. 1989). Correspondingly, there is information which indicates that the hamstrings are more active than usual in the ACL deficient knee, indicating the likelihood of additional reflex arcs between other pericapsular and capsular knee joint structures with the hamstrings (Draganich et al. 1989; Solomonow et al. 1987). This lends increased support to the role of the hamstrings as a dynamic knee joint sta­biliser.

The goal of preathletic training exercise is that through gradual introduction of increasingly com­plex knee joint activities the patient may be able to learn to rely more heavily on the knee's re­maining proprioceptive structures (Draganich et al. 1989; Elmqvist et al. 1989; Solomonow et al. 1987). In general, these activities are begun late in the re­habilitation period prior to return to athletic activ­ity, but passive cycling is one example of a pro­prioceptive training activity which could be initiated comparatively early.

5. Knee Braces

Finally, the role of knee bracing following an­terior cruciate ligament reconstruction requires comment. There are 3 basic categories of knee braces used today. Prophylactic knee braces are de­signed to prevent or reduce the severity of knee injuries. Rehabilitative knee braces are intended to allow protected motion of injured knees treated

344

Table I. A typical patellar tendon graft rehabilitation programme

Postoperative Immediately after surgery CPM 20 to 900

Don Joy rehabilitative brace 20 to 900

Active hamstring ROM Ankle AROM Crutches (nonweightbearing) 1 week CPM continued at home until ROM is full and easy Full ROM when supervised by the physical therapist Avoidance of hyperextension or active extension PREs ankle motions Cycling (operative extremity passive) Hamstring PREs Unrestricted hip exercises - avoid active quadriceps

exercises 2 weeks All of the above continued throughout rehabilitation 25% partial weightbearing with crutches Begin closed chain quadriceps exercises 3 weeks 50% partial weightbearing with crutches Progress closed chain quadriceps exercises

(include squats 45 to 900)

4 weeks 75% partial weightbearing with crutches 5 weeks Full weightbearing Discontinue rehabilitative brace B weeks Continue to progress all of the above Add isometric quadriceps exercises 45 to 900

(variable positions) Progress squats to full extension 4 months Start 00 for quadriceps activity (SLRs and 'short arc quads'

without resistance) Begin pool running 6 months Isokinetic quadriceps exercises Begin aggressive cycling Emphasise maximal strength returns at all degrees of knee

extension and at all speeds of contraction Begin normal running at 7.5 months Progress through agility drillS as strength and function

progress Resume competitive athletics No earlier than 9 months Full ROM Quadriceps strength to at least 90% of uninvolved LE No pain or swelling Successful completion of preathletic agility training

(general and sport-specific)

Abbreviations: CPM = continuous passive motion; (A)ROM = (active) range of motion; PRE = progressive resistive exercise;

SLR = straight leg raise.

Sports Medicine 12 (5) 1991

operatively or nonoperatively. Functional knee braces attempt to provide stability for unstable knees during strenuous activity (American Acad­emy of Orthopaedic Surgeons 1984).

Many surgeons will employ a rehabilitation brace immediately after surgery to permit a limited amount ofknee motion (Cawley et al. 1989). This approach was mentioned above. Several braces are available which can predictably limit flexion and extension. They are designed to permit the surgeon to prescribe the amount of knee joint excursion de­sired and enable this prescription to be altered as needed through simple adjustments.

Functional braces are also utilised to protect a stable knee with a reconstructed ACL. Many phy­sicians will encourage their patients to use a brace in this capacity during strenuous activity (Shel­bourne & Nitz 1990), but it is understood that these devices are only effective at low levels of stress (American Academy of Orthopaedic Surgeons 1984; Bessette & Hunter 1990). The demands placed on the ACL during athletic performance far exceed the levels at which functional braces have been proven to be effective (Bessette & Hunter 1990). Patients must be encouraged and educated in the reasons for maintaining a maximally strong, agile lower ex­tremity to protect their knee. A brace must be con­sidered of secondary importance.

6. Conclusion

In view of the recent literature, rehabilitation following reconstruction of the anterior cruciate ligament appears to be following specific trends. Table I outlines our basic postoperative approach as determined through review of the literature and personal experience. The recent literature has sug­gested a more accelerated rehabilitation approach which may also be effective in some circumstances. The goals of rehabilitation after ACL reconstruc­tion are early motion postoperatively, maximal strength return and continued intensive rehabili­tation efforts through advanced levels of activity. The need to avoid the complications of prolonged immobility has been discussed, in addition to the

Rehabilitation After ACL Reconstruction

importance of an aggressive strengthening and neuromuscular re-education programme.

Many important questions remain unanswered regarding the optimal way to reach the goal of a maximally functional knee following anterior cru­ciate ligament reconstruction. Perhaps the most fundamental of these is simply how much stress can a reconstructed anterior cruciate ligament safely withstand during the various stages of healing? A better understanding of these constraints would en­able optimal therapeutic efforts within the limits of the biological needs of an ACL graft.

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Sports Medicine 12 (5) 1991

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Correspondence and reprints: Philip A. Frndack, 1087 Dennison Ave, Columbus, OH 43201, USA.