The purpose of this study was to establish the return of function to an unstable knee following stabilization of the anterior deficient cruciate ligament.

15 consecutive cases of chronic anterior cruciate ligament rupture with instability were studied prior to stabilization by patellar bone-tendon-bone autograph, and again at three months post-operation and at one year post stabilization. There were two women and thirteen men in this study. All operations were performed by one of the authors (John Fleetcroft).

Peak torque, total work and average power were studied at 90°/sec and 120°/sec.

Three patients had unusually low contralateral flexor power at 120°/sec pre-operatively, these measurements were excluded from the 120°/sec results.

Our findings show an initial decrease of strength three months postoperatively; on the extensors more than on the flexors.The flexors recovered faster than the extensors.

Extensor function showed a deficit of 13% at both speeds pre-operatively. Three months following surgery this has increased to an average of 33.7% at 90°/sec and 22.8% at 120°/sec. At one year the deficit had decreased dramatically to 2.2% at 90°/sec and 0.14% at 120°/sec.

Flexor function at 90°/sec showed a deficit of 6.4% pre-operatively, 15% at three months and 1.7% at one year. At 120°/sec, pre-operative flexor deficit was 3.1%, +0.16% at three months and +4.4% at one year.

These tests demonstrate the return of function to unstable cruciate deficient knees, an important observation for those wishing to return to sport.

Defects of the anterior cruciate ligament have been treated surgically with intra- and extra-articular procedures since several decades, either as direct repair or using autografts of the hamstring or patella tendon in open or arthroscopic operations. On the other hand there are studies about successful results of conservative treatment available, too.

Casteleyn et al (1) reported about the follow up of at least five years (mean 8.5 years) of 109 patients which excluded professional and high level athletes. The evaluation of their symptoms with an IKDC score showed 23% in grade A and 50% in grade B out of four possible grades with an incidence of 5.4% secondary ACL surgery.

In an editorial article about anterior cruciate ligament reconstruction Dandy et al (2) reviewed the results of several studies about intra- and extra-articular procedures, which examined pivot-shift and restriction of activity.

Johnson et al (3) found in 87 patients with bone-patellar tendon-bone reconstruction and a mean follow up of 7.9 years 26% positive pivot shift and 25% of the patients had unrestricted activity. Sandberg et al (4) reviewed a similar group of 89 patients after seven years with 11% positive pivot-shift and 24% unrestricted activity.

In comparison to these results extra-articular procedures show a higher incidence of pivot-shift and lower levels of unrestricted activity; Odensten et al (5) report 59% clinical instability four years after Ellison procedure and 39% positive pivot-shift with only 44% unrestricted sport activity at six years after MacIntosh operation.

Over the last years extra-articular procedures were abandoned in favor for intra-articular operations.

Today bone-patellar tendon-bone grafts are widely used for these repairs.

Clancy et al (6) and Butler et al (7) have shown in animal studies a decrease of strength and mechanical properties postoperatively during an initial period of revascularisation and remodelling.

Grontvedt et al (8) look at these properties in their study about the effects of the use of a ligament augmentation device by isokinetic testing on a Biodex™ system. They measured peak torque and total work and found a deficit in the quadriceps strength in comparison to the uninjured knee of 25% at six months, 15% at one year and 10% at two years. The hamstrings improved to equal levels already after six months.

The aim of our study was to assess the mechanical properties torque, total work and average power of the hamstrings and quadriceps in order to evaluate the progress of the patients postoperatively including the above mentioned initial decrease in strength. The testing was performed with a Cybex™ machine preoperatively as well as three and twelve months postoperatively.

We tested patients who had a bone-tendon-bone anterior cruciate ligament reconstruction performed between March 1998 and January 1999. It was only a limited time window available for this study and therefore we could conduct the tests only on 15 consecutive patients. We tested two women and 13 men. Their mean age was 38.4 years (21 to 50). Injuries of the anterior cruciate ligament were confirmed by both clinical and arthroscopic examination. Indications were clinical instability, pain and / or swelling during sport or other physical activity and / or other relevant history (knee gives way). All the operations were arthroscopic assisted procedures. They were performed by only one surgeon (J P Fleetcroft). The graft was obtained from the middle third of the patellar tendon and fixed with Acufex™ interference screws.

The isokinetic tests were performed preoperatively, then three months postoperatively and one year postoperatively. The following parameter were obtained for both flexors and extensors at two speeds (90°/sec and 120°/sec): peak torque, total work and average power. At the preoperative test both injured and contralateral knees were tested, at three months and one year only the involved knee. The figures of the uninvolved knee were used as references to calculate mean deficit / progress percentages for the operated side during the course of the study.

Three patients (number 2, 6 and 14) showed at the preoperative measurements unusually low strength at the 120°/sec tests of the flexors of their uninjured knees. The figures of the uninjured knees had to be used as references in the evaluation of progress / deficits of the injured and operated knees. Therefore all calculated results of those three patients became unrealistically high and did not represent true values. As the mechanical properties of the uninjured knees were otherwise of no interest for this study we decided to exclude these patients from the 120°/sec flexor tests.

Preoperatively the extensors showed a deficit of strength (average of peak torque, total work and average power) at both speeds of 13%. This deficit worsened at three months to 33.7% at 90°/sec and 22.8% at 120°/sec. After one year strength had improved nearly to the preoperative level with a deficit of 2.2% at 90°/sec and 0.14% at 120°/sec.

Flexors: The flexors showed smaller deficits than the extensors. Preoperative figures show deficits of 6.4% at 90°/sec and 3.1% at 120°/sec. At three months the deficit at 90°/sec worsened to 15% but at 120°/sec it improved to the level of the unoperated leg (+0.16%). After one year the strength was at both speeds better than at the unoperated leg (+1.7% at 90°/sec and +4.4% at 120°/sec). The detailed deficit / progress figures for all the measured properties of our study are shown in the tables below.

Table 1 Mean deficit / progress [%]; PT = peak torque, TW = total work, Pow = average power

Table 2 Deficit / progress [%] of strength (average of peak torque, total work, average power)

The strength deficits which resulted from the anterior cruciate ligament defect improved significantly. In both muscle groups and at both test speeds the average strength of the operated knee was after 12 months at about the same level as the uninjured leg. As the flexors are to a lesser extent effected by the operation than the extensors they recovered faster; similar to the findings of Grontvedt et al (8).

The flexors showed at both speeds slightly better results than the uninvolved knee and only the extensors had still a small deficit of 0.147% (120°/sec) and 2.21% (90°/sec) in comparison to the uninjured knee after 12 months.

Further could be shown that apart from flexors at 120°/sec an initial decrease in strength occurred at the three months measurements (as also reported in [6] and [7]).

Grontvedt et al ( 8) still report about 25% weakness of the extensors after six months. In our study already at three months all groups apart from the extensors at 90°/sec (−33.7%) have results better than this (−22.8%, −15.04%, +0.17%). Grontvedt’s study shows 15% deficit after one year and 10% after two years. In comparison to this we could demonstrate nearly normal results (−2.2%, −0.14%, +1.7%, +4.4%) after 12 months. As the test speed influences the results especially during the initial period of decreased strength and Grontvedts study tested at 60 and 240°/sec this might be one reason for the different results.

The overall figures for the patients’ progress are satisfactory. They demonstrate the return of function to an initially unstable cruciate deficient knee.

We would suggest further research into the details of the initial weakness during the first postoperative months as this might have implications for physiotherapy and rehabilitation as well as surgical technique and devices.