Muscle Strength in Patients with
Unicompartmental Arthroplasty
Am. J. Phys. Med. Rehabil. 2004 Vol. 83, No. 8
Introduction
●Uicompartmental arthroplasty of the knee is an attractive alternative to high tibial osteotomy or
total joint replacement in selected patient with unicompartmental degenerative arthritis
●Osteoarthritic changes should be limited to one compartment and patients should weigh <90 kg,
have no flexion contracture,have at least 90 degrees of flexion, and have no instability or angular
deformity
●Progressing arthritis in the contralateral compartment and a shorter longevity compared with total
knee arthroplasty are considered disadvantageous.:
1.smaller implant size, less trauma caused by surgery.
2. preservation of both cruciate ligaments and bone stock.
●There are only a few studies that evaluate the function of the knee after unicondylar replacement.
Gait analysis, electromyographic analysis, evaluation of proprioception, and isokinetic testing of
the lower limb have been well established as functional analyses of the knee after partial or total
replacement
●Isokinetic strength measurements in patients after total knee arthroplasty showed that maximum
peak torques in extension and flexion are decreased approximately 50% in comparison with healthy
control subjects of the same age.
●Extension peak torque is more affected than flexion peak torque, which is indicated by an
increased flexion and extension ratio after total knee arthroplasty.
●Two studies measured isokinetic strength in patients who had unicompartmental arthroplasty for
degenerative arthritis:
1. Weidenhielm et al.6 did not show any differences.
2. Ivarsson and Gillquist7 did a similar study and also did not show diffencs
●None of these studies compared its results with healthy control subjects of the same age or tried to
correlate clinical and isokinetic results.
●The aim of the current study was to compare the isokinetic strength in flexion and extension of the
knee inpatients with unicondylar sledge prostheses and healthy control subjects of the same age and
to attempt to correlate the isokinetic results with clinical score results.
MATERIALS AND METHOD
● A total of 17 patients, 16 women and one man, with unicondylar sledge prostheses (five Endo,
Link, Hamburg, Germany; 12 Search, Aesculap,Tuttlingen, Germany; 12 were medial and five
were lateral) were examined at an average follow-up of21.5 + 8.7 mos (range, 9–36mos)
● Seven patients had surgery on the left knee and ten patients had surgery on the right knee.
● All patients participated in the hospital’s former standard rehabilitation program:1. mainly was
aimed at range of motion, 2. proprioceptive abilities.
● program consisted of 5 wks of inpatient rehabilitation (hospital and rehabilitation facility) and
12–16 additional weeks of outpatient rehabilitation (2–3 times/wk).
● No patient received specific strengthening exercises of lower limb muscles. The patients
included did not have radiologic signs of loosening or malalignment at follow-up.
● control group of 11 healthy subjects without a history of knee problems and a normal
examination was used for comparison.
● Clinical examination was done using the Hospital for Special Surgery score, the Knee Society
score, and the patellar score. All three are common clinical scores that assess objective
measures.
● Isokinetic evaluation of knee extensor and flexor muscles was doneusing a Cybex 6000
dynamometer.
● After sufficient warm-up, measurements were recorded at angular velocities of 60 and 180
degrees/sec, using the computerbased data acquisition system.
● Statistical analysis was done with a commercial program (Stat View,Version 5.0, SAS Institute,
Heidelberg,Germany). Mann-Whitney U test was used to compare control and patient groups
Wilcoxon’s signed-rank test was done for intraindividual comparison of both legs in each group
RESULTS
●The average age of the patients was 62.5 +8.3 yrs (range, 50 –77 yrs). The average height of the
patients was 167+7.6 cm, and the average weight was 84.6+20.3 kg.
● The control group consisted of six men and five women with an average age of 69.1 + 5.5 yrs
(range, 60 –75 yrs). The average height of the control subjects was 168.5 + 8.8 cm (women,
165.6+ 4.7 cm;men, 171.2+7.2 cm), and their average weight was 72.2+10.6 kg (women, 67.4 +
11.8 kg; men, 76.2+ 8.5 kg).
●There were no significant differences in demographics between sexes in the control group or
between patient and control groups (P > 0.05).
●Statistical analysis of the clinical results revealed neither a difference between the types of
prostheses.
●Hospital for Special Surgery score, P = 0.355; Knee Society score, P = 0.834; patellar
score, P =0.53) nor a difference between implantation sites (medial vs. lateral; Hospital for
Special Surgery score, P = 0.425; Knee Society score, P =0.371; patellar score, P =0.33).
Therefore, the following results comprise the localizationsand prostheses.
●The control group scored nearly maximum results in clinical examination. They achieved an
average Hospital for Special Surgery score of 93.1 + 10.3 of 100 points and a Knee Society
score of 192.3+14.6 of 200 points. The patellar score averaged 29.6+ 1.5 of 30 points, and the
visual analog scale for pain averaged 9.9 +0.3 of 10 points. The patients’ clinical results were
significantly lower (P <0.05) than the clinical results of the control subjects.
●Table 1 shows the patients’ results on the Short Form 36 Health Questionnaire. Comparing
patients and control subjects, only the following items differed significantly: physical functioning
(P = 0.003), role limitation due to physical problems (P = 0.0117), and bodily pain (P = 0.0293)
●Peak flexion torques at 60 and 180 degrees/sec in patients were significantly lower compared
with the control subjects (Table 2).The patients achieved only approximately 70% of normal
flexion strength. In maximum isokinetic strength in extension at 60 and 180 degrees/sec, the
patients achieved only approximately 70% of normal strength.
●The average flexion and extension ratios of maximum peak torque in patients did not differ from
those in control subjects (Table 2).
●Correlation analysis of isokinetic data and clinical score results or isokinetic data and eight
different Short Form 36 items, respectively, revealed no statistically significant correlation
coefficient.
DISCUSSION
●To the current authors’ knowledge, only two reports can be found in the literature that address the
muscle strength
●.Ivarsson and Gillquist were able to prove a faster recovery of muscle strength in the
postoperative course in patients who had unicompartmental knee arthroplasty compared with
patients who had high tibial osteotomy.
●The results 6 mos postoperatively were better in the patients who were treated with
unicompartmental arthroplasty than they were 12 mos postoperatively in the patients treated with
high tibial osteotomy.
●The current authors showed that after unicompartmental knee arthroplasty, patients had a clear
deficit of peak torque of approximately 30% in extension and flexion at 60 and 180 degrees/sec
compared with the control group.
●Isokinetic strength measurements in patients after total knee replacement showed that
maximum peak torques in extension and flexion are decreased approximately 50% in
comparison with healthy control subjects of the same age.
●The persisting extensor weakness was thought to be related to anterior cruciate ligament
resection because patients with an anterior cruciate ligament rupture have similar quadriceps
deficits.
●The present study has two methodological limitations:
1. retrospective study design
2. the different female-to-male ratio in the patient and control group.
●Unicompartmental arthroplasty seems to fail to restore age. This is most probably attributable
to the preoperative phase of reduced activity because patients with osteoarthritis have been
reported to already have decreased muscle strength.
●The underlying reasons are probably the smaller operative approach that does not injure the
quadriceps muscle and the preservation of the anterior cruciate ligament that prevents
quadriceps.