Survivorships of Small Cementless Femoral Stems are Similar to Mid-Size Stems. A Case-Control Study on Four Hundred and Twenty Total Hip Arthroplasties

Stanislas Gunst1-4*, Anthony Viste1-4, Muriel Rabilloud5, Romain Desmarchelier1-4 and Michel Henri Fessy1-4 1Hospices Civils de Lyon, Centre Hospitalier Lyon-Sud, Chirurgie Orthopédique, 165 Chemin Grand Revoyet, 69495 Pierre-Bénite, France 2 Université de Lyon, 69622 Lyon, France 3Université Claude Bernard Lyon1, 69100 Villeurbanne, France 4IFSTTAR, UMRT_ 9406, Laboratoire de Biomécanique et Mécanique des Chocs, 69675 Bron, France 5Hospices Civils de Lyon, Service de Biostatistique, F-69003, Lyon, France


Introduction
Initially developed to be implanted in young patients [1], cementless THA (Total Hip Arthroplasty) are now commonly used, with a proportion that recently surpassed cemented THA in England (39.1% in 2016 [2]) and Australia (63.3% in 2015 [3]). Several series reported excellent long-term survival [4][5][6][7][8], up to 96% at a 23 years follow up with the CorailTM stem (DePuy Synthes, Saint Priest, France) [8]. However, few studies reported the influence of the stem size on the clinical outcomes after THA [9][10][11][12]. The British National Joint Register suggested that the revision rate of the Corail stem was higher with small femoral stems (8 to 10) compared to mid-size stems (11 to 13) [12]. The purposes of our study were to assess the clinical outcomes and survivorships of standard small stems (exposed group) to standard mid-size stems (control group) at a mid-term follow-up. We hypothetized that the use of small stems was not associated with a higher risk of revision compared to mid-size stems.

Patients and Methods
We retrospectively recorded 807 patients who underwent

Surgical Technique
Procedures were all performed through a posterolateral approach by the same senior surgeon. Femoral preparation technique aimed for optimal filling of the trial broaches with good vertical and rotational stability keeping a bed of cancellous bone.
A standard rehabilitation protocol was initiated after surgery with full-weight bearing allowed immediately.

Complications and Revisions
Seven dislocations were identified (six in the patients with a  (Table 2).

Figure 2:
Radiographs of a 56 years old man who had a stem revision for aseptic loosening. Immediate (Fig 2A) and three years post-operative (Fig 2B) X-rays with development of femoral lines in Gruen's zones 1, 2, 3 and 6. in the mid-size group, p=0.09) (Figure 4)
Our results are consistent with these previous series, with an Only standard Corail stems were included as lateralised stems previously demonstrated a higher risk of loosening [18,19].
Demey et al. [20] showed that the use of a collared Corail stem increased the horizontal and vertical stability. In our series, we only implanted collared stems, while most of stems were collarless for Jameson et al [12]. Two cases of stem aseptic loosening were recorded in our study (13% of the causes for revision). This was consistent with the results of Jameson et al [12] with a revision rate of 16.5% for stem aseptic loosening. At 15-year, Engh et al. [11] calculated the overall survivorship of the stem was 98%.
Survivorship was not significantly different among the different stem sizes (p=0.4). Vresilovic et al. [9] reported the survivorship of 296 femoral stems at 2-year follow-up and did not find any significant difference according to stem size. Our study had several limitations. First, we did not perform radiological analysis, as it was not the purpose of this study but to focus on survivorship. Second, the study was retrospectively performed. The strengths were its homogeneity, as the same senior surgeon performed all procedures and the mid-term follow-up.
The influence of stem size on revision rate is controversial. In the current study, small size stems (8 to 10) were not associated with higher revision rates compared to mid-size stems (11 to 13).
Further studies including a larger sample size, at a longer followup, with radiological analysis must be performed in the future.