Defining 'undersizing' in short-stem total hip arthroplasty: the importance of sufficient contact with the lateral femoral cortex.

INTRODUCTION: Undersizing is 1 of the main reasons for early implant failure. Adequate sizing in short-stem total hip arthroplasty can be challenging and, so far, lacks key decision criteria. METHODS: We included 191 calcar-guided short stems. All patients underwent standardised digital anteroposterior imaging pre- and post-surgery and during follow-up. Preoperative planning was performed digitally. Planned stem sizes were retrospectively assessed and compared with the implanted sizes. Additionally, adequate sizing was analysed by determining whether the stem made intraoperative contact with the lateral distal femoral cortex. Implant migration was assessed by Ein-Bild-Roentgen-Analysis Femoral-Component-Analysis 5 years after surgery. Influence of different Dorr types and postoperative centrum-collum-diaphyseal angle (CCD) categories on lateral femoral cortical contact were analysed. Additionally, the Harris Hip Score (HHS) was assessed at final follow-up. Stem-revision rate was documented. RESULTS: Implanted stems were at least 2 sizes smaller than those at the preoperative planning in 49 (25.7%) cases. The stem made contact with the lateral distal femoral cortex in only 130 hips (68.1%). Mean subsidence was significantly higher in the no-contact group (2.07 mm, range -7.7 to 1.7) than in the contact group (1.23 mm, range -4.5 to 1.8) at the final follow-up (p = 0.0018). Stems at least 2 sizes smaller than those at preoperative planning showed a significantly higher prevalence of non-contact (46.9% vs. 26.8%) (p = 0.009). Those undersized stems were more likely found in varus hips. No influence of the Dorr classification and the different CCD categories on the probability of achieving sufficient cortical contact was found. HHS showed no intergroup differences. CONCLUSIONS: Stems that did not make intraoperative contact with the lateral femoral cortex showed significantly increased axial migration at mid-term follow-up. Thus, the investigated criteria regarding the definition of undersizing in short-stem THA should be acknowledged. No obvious mid-term consequences were noted regarding revision rate. Long-term results are mandatory.

Cemented short-stem total hip arthroplasty: Characteristics of line-to-line versus undersized cementing techniques using a validated CT-based finite element analysis.

Short stems are becoming increasingly popular in total hip arthroplasty as they preserve the bone stock and simplify the implantation process. Short stems are advised mainly for patients with good bone stock. The clinical use of short stems could be enlarged to patients with poor bone stock if a cemented alternative would be available. Therefore, this study aimed to quantify the mechanical performance of a cemented short stem and to compare the "undersized" cementing strategy (stem one size smaller than the rasp) with the "line-to-line" technique (stem and rasp with identical size). A prototype cemented short stem was implanted in eight pairs of human cadaveric femora using the two cementing strategies. Four pairs were experimentally tested in a single-legged stance condition; stiffness, strength, and bone surface displacements were measured. Subject-specific nonlinear finite element models of all the implanted femora were developed, validated against the experimental data, and used to evaluate the behavior of cemented short stems under physiological loading conditions resembling level walking. The two cementing techniques resulted in nonsignificant differences in stiffness and strength. Strength and stiffness as calculated from finite element were 8.7 ± 16% and 9.9 ± 15.0% higher than experimentally measured. Displacements as calculated from finite element analyses corresponded strongly (R 2 ≥ .97) with those measured by digital image correlation. Stresses during level walking were far below the fatigue limit for bone and bone cement. The present study suggests that cemented short stems are a promising solution in osteoporotic bone, and that the line-to-line and undersized cementing techniques provide similar outcomes.

Incidence of heterotopic ossification in minimally invasive short-stem THA using the modified anterolateral approach.

INTRODUCTION: Heterotopic ossification (HO) is known to be a common complication after total hip arthroplasty (THA). The minimal invasive (MIS) modified anterolateral approach has become popular in combination with a short stem. We analysed the incidence of HO following short-stem THA using this approach in combination with a postoperative administration of nonsteroidal anti-inflammatory drugs (NSAIDs). MATERIALS AND METHODS: 216 short stems were implanted in 162 patients. NSAIDs were administered for 2 weeks after surgery in 154 patients (95.1%). Standardised pre- and postoperative radiographic imaging was done at 2-year follow-up. HO was analysed according to the Brooker classification. Influence of age, gender, body mass index (BMI), and blood transfusion were analysed. Harris Hip Score (HHS) and visual analogue scale (VAS) of satisfaction were assessed. Operation time and blood-transfusion rate was documented. Short-term gastrointestinal side effects were recorded. RESULTS: The overall incidence of HO was 7.8% (16 cases). HO Brooker type 3 and 4 occurred in only 1 case (0.5%). No correlation with age, gender or BMI was revealed. HHS improved largely from 45.8 (SD 15.9) before surgery to 98.1 (SD 4.7) after a minimum of 2 years. At that point VAS satisfaction was 9.7 (SD 0.9). Mean operative time was 45.8 minutes (SD 18.7). 12 patients (7.4%) received at least 1 blood-transfusion. Gastrointestinal side effects occurred in 13 of 154 patients (8.4%). CONCLUSIONS: The combination of short-stem THA, the MIS modified anterolateral approach and a postoperative application of NSAIDs resulted in the effective prevention of HO and excellent clinical results.

Radiographic alterations in short-stem total hip arthroplasty: a 2-year follow-up study of 216 cases.

INTRODUCTION: In recent years a variety of short-stems have been introduced. Stable osteointegration is a key factor for a satisfactory long-term result. The purpose of this study was to evaluate postoperative radiological alterations and subsidence, as a result of using a newly developed device, over a 2-year follow-up. METHODS: 216 short-stems were implanted in combination with a cementless cup. Patients were allowed full weight-bearing on the first day postoperatively. Pre- and postoperative x-rays were done using a standardised technique. Radiological alterations, such as bone resorption, radiolucency, osteolysis and cortical hypertrophy were detected and located using modified Gruen zones, and subsidence was measured via a conventional digital technique over a 2-year follow-up. In addition, Harris Hip Score (HHS), rest pain and load pain on the visual analogue scale (VAS) were assessed respectively. RESULTS: At 2-year follow-up 6 stems (2.9%) showed nonprogressive radiolucent lines with a maximum width of 2 mm. Resorption of femoral bone stock was detected in a total of 8 cases (3.9%). Femoral cortical hypertrophy was seen in a total of 9 hips (4.4%). No patient showed osteolysis. A measureable subsidence of at least 2 mm was observed in a total of 15.7% (32 cases) after 6 weeks, corresponding to an initial settlement given full weight-bearing ambulation. Only 1.1% (2 cases) showed further progression at the 6-month follow-up, whereas at the 1- and 2-year follow-ups no further subsidence was observed. After 2 years HHS was 98.1 (65.0-100.0), rest pain on the VAS was 0.2 (0.0-7.0) while load pain was 0.4 (0.0-7.0). CONCLUSIONS: The results of this radiographic analysis give support to the principle of using metaphyseal anchoring, calcar guided short-stems. The low incidence of bony alterations after a follow-up of 2 years indicates a physiological load distribution. After mild initial subsidence a stable osteointegration can be achieved over time.