Are Preoperative Measures of Knee Stability, Strength and ROM Predictive of Results Following ACL Reconstruction?

MP McHugh, TF Tyler, GW Gleim, EB Hershman, SJ Nicholas

NISMAT, Lenox Hill Hospital.

Preoperative screening of patients undergoing ACL reconstruction is thought to be important in predicting surgical outcome. The purpose of this study was to quantify the association of preoperative measures of knee extension(KE) ROM, strength and stability with measures repeated six months postoperative. KE ROM (goniometrically in supine with feet elevated), KE strength (isokinetically at 60 deg./s), and knee stability (KT1000 side-side difference at 89 N and manual maximum) were assessed in 94 patients within two weeks prior to ACL reconstruction and again six months post-op. All patients underwent single incision endoscopic reconstruction using an autogenous bone-patellar tendon-bone graft.

RESULTS:

1. Pre-op KE ROM was correlated with KE ROM six month post-op (r=0.27, p=0.01). Patients with full extension pre-op (equal to contralateral knee) had 1.3 +/- 0.5 deg. loss post-op (84%<5 deg.); patients lacking 1-4 deg. pre-op had 3.8 +/- 0.7 deg. loss post-op (61%<5 deg.); patients lacking >= 5 deg. pre-op had 3.8+0.8 deg. loss post-op (63%<5º); ANOVA p<0.01.

2. Pre-op KE strength measures were not significantly correlated with strength six months post-op (r=0.2, p=0.09). Nine patients were not tested at six months due to knee pain. Forty nine patients with clinically significant weakness (pre-op deficit >= 20%) had a 38 +/- 3% deficit at six months. Twenty two patients without clinically significant weakness (pre-op deficit < 15%) had a 32 +/- 2% deficit six months post-op (insignificant between group difference, p=0.09).

3. KT1000 measures decreased with surgery from 3.2 +/- 0.3 mm to 1.6 +/- 0.3 (p=0.001) at 89 N and from 5.4 +/- 0.3 mm to 2.6 +/- 0.4 mm (p=0.001) with manual maximum. Pre-op KT1000 measures were significantly correlated with post-op measures (r=0.43, p=0.001 at 89N; r=0.4, p=0.001 with manual maximum).

CONCLUSIONS:

1. Preoperatively even a slight loss of extension (1-4 deg.) results in difficulty regaining extension postoperatively.

2. Preoperative knee extension strength is not a good indicator of strength return following ACL reconstruction.

3. The ability to surgically restore normal arthrometric knee stability is moderately limited by preoperative knee instability. Residual laxity may be a function of stretch-out of secondary restraints preoperatively.

   In conclusion, a decision to delay surgery should be based on the presence or absence of full extension (relative to the contralateral knee) and not actual degrees loss of extension.

Transactions of the 2nd World Congress on Sports Trauma/AOSSM 22nd Annual Meeting 1996, p. 735.