Magnitude of Limb Lengthening After Primary Total Knee Arthroplasty

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Abstract

Patients will often perceive a change in lower limb length after total knee arthroplasty (TKA). From this observed finding, we asked how frequently does a change in limb length occur after TKA. Preoperative and postoperative full-length standing radiographs were obtained for 102 knees in 98 patients who underwent TKA. Digital radiography software was used to measure the mechanical axis and limb length of the operative and nonoperative legs. Overall, 83% of the knees measured showed an increase in limb length after TKA. Preoperative varus alignment was associated with an average lengthening of 5.2 mm. Preoperative valgus alignment was associated with an average lengthening of 8.4 mm. Patients with a valgus deformity greater than 10° demonstrated the greatest average lengthening. It is the conclusion of this study that limb lengthening occurs frequently after TKA, back to a length similar to the nonoperative limb.

Section snippets

Patients and Methods

We retrospectively identified patients by reviewing the consecutive case logs of 2 experienced total joint surgeons between March 2007 and October 2007. Patients were included if they had preoperative and postoperative, full-length, standing radiographs, with a 10-cm radiographic marker. Because of ordering errors on some patients' films, approximately 10% of patients on the case logs reviewed did not have either preoperative or postoperative leg length films taken. The requisite films had been

Results

In this study, 85 (83.3%) of the 102 knees comprising the entire study group showed increased limb length after TKA (Table 2). Average lengthening was 6.3 mm (SD, 6.85 mm; range, −11.0 to 24.0 mm). Mean postoperative alignment was 0.98° (SD, 3.15°).

Fifty-two (78.7%) of 66 knees in the varus group showed increased limb length after TKA. The average lengthening was 5.2 mm (SD, 5.76 mm; range, −6.8 to 18.2 mm). Average mechanical alignment preoperatively was 8.7° of varus preoperatively and 2.1°

Discussion

Studies in the orthopedic surgery literature describe the problems resulting from limb-length changes after total hip arthroplasty (THA) 7, 8, 9, 10. Since the basic principles of joint restoration are similar, we investigated the frequency and characteristics of limb-length changes occurring after TKA. Our aims for this study were to (1) detect the frequency of limb lengthening after TKA, (2) determine if preoperative varus versus valgus deformity influences postoperative limb length, (3)

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    When assessing the LLD after primary TKA, Lang et al noted an increased limb length in 83% of patients undergoing TKA compared with the 63% lengthened and 37% shortened lengths in our study. They also noted during their study that valgus deformity preoperatively was associated with an 8.4-mm lengthening compared with a mean lengthening of 5.2 mm for varus deformity [6]. For all patients in their study with lengthening, there was correction of the valgus or varus, with no lengthening in patients without preoperative valgus/varus deformity.

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    One possible underlying variable is change in limb length. LLD after TKA is mostly due to lengthening of the operated limb.7–9 Severity of osteoarthritis and preoperative coronal plane deformity (varus/valgus) plays major role in postoperative limb length.5

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The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2011.06.008.

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