Modular neck stems in total hip arthroplasty: current concepts

Modular neck (MN) implants can restore the anatomy, especially in deformed hips such as sequelae of development dysplasia. Early designs for MN implants had problems with neck fractures and adverse local tissue, so their use was restricted to limited indications. Results of the latest generation of MN prostheses seem to demonstrate that these problems have been at least mitigated. Given the results of the studies presented in this review, surgeons might consider MN total hip arthroplasty (THA) for a narrower patient selection when a complex reconstruction is required. Long MN THA should be avoided in case of body mass index > 30, and should be used with extreme caution in association with high offset femoral necks with long or extra-long heads. Cr-Co necks should be abandoned, in favour of a titanium alloy connection. Restoring the correct anatomic femoral offset remains a challenge in THA surgeries. MN implants have been introduced to try to solve this problem. The MN design allows surgeons to choose the appropriate degree and length of the neck for desired stability and range of motion. Cite this article: EFORT Open Rev 2021;6:751-758. DOI: 10.1302/2058-5241.6.200064

Bilateral neck fracture in bimodular femoral stem after primary total hip arthroplasty: a case report

Background Bi-modular stems were introduced in primary total hip arthroplasty (THA) to enable better control of the femoral offset, leg length, and hip stability. Despite numerous reports on modular femoral neck fractures, some designs are still marketed worldwide. While the risk factors for the sudden failure are multifactorial and mostly known, the timing of this new THA complication is not predictable by any means. Case presentation In this report, the literature regarding one of the most popular bi-modular stems with specific neck-stem coupling (oval Morse taper) is reviewed and illustrated with a case of bilateral modular neck fracture in a patient with idiopathic aseptic necrosis of femoral heads treated with primary bi-modular THA. Because of bilateral modular femoral neck fracture, which occurred 3 years on the left side and 20 years after implantation on the right side, the patient required a total of 6 revisions and 208 days of hospitalized care. Conclusion To our knowledge, this is the first report of bilateral modular neck fracture in a single patient. Even though the same surgeon performed both operations and used the same neck length and orientation, fractures occurred with a 17-year time difference after implantation. This shows that we cannot predict with certainty when a fracture might occur. Orthopaedic surgeons should use bi-modular stem designs for primary THA very cautiously.

Hip hemiarthroplasty with modular neck: is it useful in residents’ learning curve? A prospective clinical trial

Background: The number of femoral neck fractures (FNFs) worldwide will drastically increase in the next few decades, reaching 6.3 million by 2050. In the future, therefore, newly-qualified orthopaedic surgeons will treat this kind of injury more frequently than in past decades. This prospective observational study aims to assess whether hip hemiarthroplasty with modular neck, performed via the Hardinge approach, can be safely carried out by orthopaedic residents. Methods: Patients referred to our Level I trauma centre, between January 2016 and June 2017, with displaced intra-articular femoral fractures, were prospectively recruited. All patients underwent cemented modular bipolar hip hemiarthroplasty (Profemur Z, MicroPort Orthopedics Inc., Arlington, TN, USA) via the Hardinge approach, with the patient positioned in lateral decubitus. The surgical procedures were performed by the same surgical and anesthesiology team, under spinal anaesthesia. All patients underwent clinical and radiographic follow-up up to 24 months. Complications and re-operations were recorded. Clinical evaluation was performed using the Harris Hip Score (HHS), Osteoporosis Quality of Life Questionnaire QUALEFFO-41 and EuroQol-5D (EQ-5D) questionnaire. Anteroposterior pelvis x-rays were performed preoperatively, postoperatively and at 1, 3, 6, 12 and 24 months follow-up. Results: 118 patients met the inclusion criteria (male: 50; female: 68; mean age: 74.3 years; range 65–88 years) and were included in the current study. 67 patients out of 118 (56.8%) were managed by senior orthopaedic surgeons (Group A), whereas the remaining 51 patients out of 118 (43.2%) were treated by orthopaedic residents (Group B). Hip hemiarthroplasties performed by senior surgeons showed the prevalent use of straight (short or long) necks, whereas, in surgical procedures performed by residents, there was a significantly higher use of varus/valgus, anteverted or retroverted necks. The overall complication rate was significantly higher in Group-B patients, compared with Group-A patients ( p = 0.002). The length of hospital stay and the mean clinical scores at 24 months follow-up showed no significant differences. Conclusions: Hip hemiarthroplasty with modular neck can be safely employed during the learning curve of orthopaedic residents. Great efforts, however, should be made in future to improve residents’ training in the management of FNFs.

Systematic review of primary total hip arthroplasty using titanium-titanium modular-neck prostheses: the true risk of revision

Aims: Modular-neck femoral implants are used to enable more variability in femoral neck version, offset and length. It has been reported that these implants carry a higher rate of revision. The aim of this review was to assess the overall and cause-specific revision rate of titanium-titanium alloy modular-neck implants in primary total hip arthroplasty (THA). Methods: A systematic review was conducted following PRISMA guidelines and utilising multiple databases. All results were screened for eligibility. Studies published from 2000 onwards, using a current-generation, titanium-titanium, modular-neck implant were included. Overall and cause-specific revision rates were analysed, comparing to fixed-neck prostheses where applicable. Results: 920 studies were screened. After applying exclusion criteria, 23 were assessed in full and 14 included. These consisted of 12 case series and 2 joint registry analyses. 21,841 patients underwent a modular-neck implant with a weighted mean follow-up of 5.7 years, mean age of 62.4 years, and average body mass index (BMI) of 28.4kg/m2. The overall revision rate was 3.95% and 2.98% for modular and fixed-neck prostheses, respectively. For studies with >5 years follow-up the mean revision rate was 3.08%. There was no difference in cause-specific revision rates by implant design. Mean improvement in Harris Hip Score was 41.9. Conclusions: At medium-term, revision rates for titanium-titanium primary modular-neck THA are acceptable. These prostheses are a sensible management option in patients with considerable anatomical hip deformity not amenable to correction with standard fixed-neck implants. Patients of male gender, high BMI and requiring prostheses with a larger neck, offset or head are at higher risk of implant failure.