Better Outcomes in Severe and Morbid Obese Patients ( BMI > 35 kg / m 2 ) in Primary Endo-Model Rotating-Hinge Total Knee Arthroplasty

1. Introduction

Constrained rotating-hinge knee prostheses are a useful orthopaedic tool in the treatment of advanced tibiofemoral deformities and severe bone and ligament defects [1–3]. The new rotating models attempt to avoid torsional stress which produces premature loosening, and to reduce the patellofemoral tension, characteristic of nonrotating constrained prostheses [1, 2]. Few studies have been published [4–9] regarding the primary indication of the Endo-Model rotating-hinge implant (Waldemar Link GmbH & Co), with most research focusing on its use in revision surgery [3–5, 9–12]. The previous generation of this implant was associated with several complications, being patellofemoral pain one of the most frequent [2, 6–9, 12]. Actual implant includes an anterior femoral shield with the aim to solve this problem. This paper reports the outcomes obtained and the complications which arose when using the Endo-Model rotating-hinge implant for primary total knee replacement.

2. Patients and Methods

A descriptive observational study with prospective followup was performed over a three-year period, from January 2006 to January 2009. During this time 120 primary cemented Endo-Model rotating hinge prostheses (Waldemar Link GmbH & Co) were implanted in patients with degenerative knee joint disease. A total of nine prostheses were excluded from the final analysis: six were lost to followup and there were three exitus. Minimum follow-up time established was one year. The mean admission time was 6.1 days, while the mean follow-up time in the series was 28 months [17; 36].

The Endo-Model is a cemented rotating knee prosthesis with a long stem and a central hinge system that enables controlled flexion and rotation, which can be converted intraoperatively into a constrained system with an antiluxation device. The model includes an anterior femoral shield, which, in theory, minimizes the mechanical tension that can arise in the patellofemoral compartment.

The study included 111 surgical prostheses (14 bilateral). Gender distribution was 84 women and 27 men, with a mean age of 72.77 years. The mean BMI was 30.81 kg/m² (median: 31.1 [27.3; 33.3]). As regards the preoperative mechanical axis 51 patients (46%) presented a valgus deformity and 60 (54%) varus deformity (Table 1).

Table 1

Baseline data. Results are expressed as mean (SD) for quantitative data and as $n$ (%) for qualitative data.

		$N=111$
Sex	Female	$84\mathrm{\hspace{0.17em}\hspace{0.17em}}(75.7\%$
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