Abstract
Modular hip stems offer many advantages in revision arthroplasty. However, the region of modularity is prone to failure. Fracture of the non-cemented fluted tapered titanium Modular Prosthesis (MP) stem is relatively rare. We present here a case of a distal non-traumatic fracture of the MP stem and review the previously reported cases. A 53-years old, relatively active, male patient with a body mass index (BMI) of 37 kg/m2 had a fracture of the non-cemented MP stem on the left side after five years without complaints. The BMI was 45 at the time of implantation of the MP stem. His weight was significantly reduced, but the stem failed and fractured at an atypical site, quite distal to the modular junction. The broken stem with a relatively small diameter had been exchanged to a larger one. Fracture of the non-cemented fluted proximally-modular distally-tapered titanium MP stem might occur after years. Even in cases of good bone quality of the proximal femur, patient BMI and activity level should be considered when selecting the stem diameter. Furthermore, proximal bone loss of the femur should be considered as a potential cause of failure.
Keywords: Revision hip arthroplasty, Implant failure, Non-cemented modular stem, Stem fracture
1. Introduction
Modular hip stems offer many advantages in revision arthroplasty, particularly in cases of substantial bone loss of the proximal femur. However, the region of modularity is prone to fail, with a risk of fracture up to 18.5%.1 Previous reports had identified some potential factors for stem fracture such as the lack of proximal cortical support, smaller diameters, the use of extended trochanteric osteotomy (ETO) and higher body mass index (BMI).1,2 Since the introduction of the non-cemented fluted tapered titanium Modular Prosthesis (MP) stem in 1993 (Waldemar Link, Hamburg, Germany), good to excellent mid-term to long-term survivorship has been achieved.3, 4, 5, 6, 7 Over the last years, a fracture of the MP stem has been reported around the modular junction or with reasonable causes in rare individual cases.3,4,6,8, 9, 10 We present here a case of a non-traumatic fracture of the MP stem in a region of good bone quality distal to the modular junction and the proximal bone loss in the light of previously reported cases.
2. Case report
A 53-years old male patient with a BMI of 37 kg/m2 (height 170 cm, weight 110 kg) who had an aseptic stem revision on the left side at our specialized high-volume hospital five years ago (October 2012), due to stem loosening of an externally implanted total hip arthroplasty (THA) in 2010. The cementless stem was loose and had been removed without bone loss. The surgeon decided for the revision using a cementless MP stem with a diameter of 12 mm due to intraoperative stability regardless of the weight or BMI of the patient. The patient presented at our outpatient clinic in November 2017 with a painful left hip of only three weeks' duration once he had lifted a heavy umbrella. Until three weeks ago, he was free of pain or any other complaint and did well so far. There was no traumatic incident before the symptom onset. However, he had to use two crutches due to the worsening pain with limping. The clinical examination revealed a very painful and limited internal rotation of the left hip with an evident tenderness over the upper and mid-thigh. The range of motion of the left hip was as follows: 0-0-100° for extension/flexion, 40-0-20° for abduction/adduction and 40-0-0° for external rotation/internal rotation.
Interestingly, the BMI at the time of first hip revision in 2012 was 45 kg/m2. Otherwise, the patient was relatively active, but with known hypertension, diabetes mellitus, and chronic obstructive pulmonary disease. The radiographic examination of the pelvis and left hip showed a slightly oblique fracture of the MP stem, entirely at the middle, with some lucency of the metaphyseal region proximally (Fig. 1A). The stem had been revised to a longer one with a larger diameter in December 2017 (Fig. 1B). While an intraoperative loosening of the proximal part of the stem was noted, which had been easily removed without special instruments, the distal portion was well-fixed. A reaming, using trephines with successively increased diameters over the distal stem, had to be utilized. The extraction of the distal part was performed very carefully to avoid an intraoperative periprosthetic fracture and was very laborious. Considerable distal bone ongrowth had been demonstrated on this removed part (Fig. 2). At 18 months follow-up, the patient is satisfied and free of pain.
Fig. 1.
A) The oblique fracture of the MP stem, approximately 4 cm distal to the modular junction with some lucency of the metaphyseal region proximally. B) Following the revision to a longer MP stem with a larger diameter in December 2017 (length: 210 mm, diameter 16/18 mm).
Fig. 2.
A) The removed stem with one of the used trephines. B) The distal part of the stem showing an obvious bone ongrowth.
3. Discussion
Fluted tapered titanium modular stems have in general a better chance to survive, showing less stress shielding compared to fully porous stems.1 However, the area around the modular junction is more susceptible to break and fail. We reviewed the literature and extracted the available data reporting on fractures of the non-cemented MP stem (LINK, Hamburg, Germany) and could able to find six cases (Table 1). The first case was a fracture of a custom-made stem for a dysplastic hip which was the only fractured stem among 143 hips reporting on 2–6 years follow-up following hip revisions using the Link MP stem in cases presenting with proximal bone loss of the femur. Here, the report included no further individual information about the patient.3 A case report presented the second case of a 48 years old female patient with a fracture of a 14 mm MP stem at the proximal portion of the middle third after 28 months. This patient had a massive proximal bone loss with a severe deficiency of the lateral cortex. Fracture analysis of this stem yielded evidence of a fatigue fracture that initiated laterally.8 The third stem had a 14 mm diameter and had broken just below the modular junction in a very obese man (145 kg) with a proximal bone loss. This was the only stem fracture in a series of 97 hips with a minimum of two years of follow-up.4 A further case report presented four stem fractures from different companies, including one 14 mm MP stem. It occurred typically at the modular junction after 84 months in a 58 years old woman with a BMI of 34.5 kg/m2.9 The next series comprising of 63 patients reporting on the outcome of MP stem after ten years had only one fracture of a 10 mm custom-made stem in a thin female patient (BMI 19 kg/m2) with severe osteoporosis and proximal bone loss after 48 months.6 The last stem fracture occurred after five years of a 14 mm MP stem quite distally. However, the patient had a non-united fracture of the femur directly proximal to the stem fracture site, and a poor proximal apposition of the stem had been observed.10 In our patient, there was no extensive loss of the bone stock proximally. Potential causes of the proximal bone loss might be the absence of absolute stability. Further causes are periprosthetic joint infection (PJI) which has been excluded through a preoperative aspiration or metallosis, which was not observed intraoperatively. He had very thick diaphyseal cortices with a narrow medullary canal and the 12 mm stem had survived five years despite a BMI of 45 kg/m2 at the time of surgery. However, we believe that the combination of a proximal loosening and the high BMI led to increased biomechanical stress of the well-fixed distal part of the stem resulting in its non-traumatic fracture in the current case. This would be confirmed through a metallographic and microscopic examination of the broken stem parts which, unfortunately, has not been performed in our case. Kilian et al. have analyzed the fracture of two similar modular tapered stems and concluded that stems with splines having decreased taper angles might be at increased risk of failure.11
Table 1.
The reported fractures of the non-cemented MP stem (LINK, Hamburg, Germany) in the literature.
| Year (Reference) | Age | Gender | BMI (kg/m2) | Stem diameter | Stem length | Survival | Fracture site | Bone quality/Notes |
|---|---|---|---|---|---|---|---|---|
| 20033 | ? | ? | ? | ? | ? | ? | ? | Custom-made stem for dysplasia |
| 20078 | 48 years | Female | 24 | 14 | ? | 28 months | Middle1/3, proximally | Proximal bone loss with a defective lateral cortex |
| 20094 | ? | Male | 145 kg | 14 | ? | ? | Just below the modular junction | Bone loss (Mallory B3) |
| 20119 | 58 years | Female | 34,5 | 14 | 335 mm | 84 months | At the modular junction | Lateral cortical defect |
| 20136 | ? | Female | 19 | 10 | ? | 46 months | ? | Custom-made stem and osteoporosis with proximal bone loss |
| 201510 | ? | ? | ? | 14 | 210 mm | 5 years | Distally | Fracture non-union with poor proximal apposition of the stem |
| 2019 (Current study) | 53 years | Male | 37 | 12 | 180 mm | 5 years | Middle1/3 | Only moderate proximal bone loss |
? = Unavailable data.
4. Conclusion
Fracture of the non-cemented fluted proximally-modular distally-tapered titanium MP stem might occur after years. Even in cases of relatively good bone quality of the proximal femur, patient BMI and activity level should be considered when selecting the stem diameter. Furthermore, proximal bone loss of the femur should be considered as a potential cause of failure. During revision, further reaming of a narrow medullary canal to accommodate a larger cementless MP stem is recommended in selected patients to avoid stem failure.
Ethics approval and consent
Approval from the ethics committee in Hamburg was obtained. The patient has given an informed consent for the case report to be published.
Conflicting interests
We have no conflict of interest. Outside the manuscript, TG reports personal fees from Waldemar Link Germany, Zimmer USA, and Ceramtec.; and MC from Waldemar Link Germany.
Funding
No sources of funding.
Contributor Information
Hussein Abdelaziz, Email: hussein.abdelaziz@helios-gesundheit.de.
Christian Ansorge, Email: Christian.ansorge@helios-gesundheit.de.
Thorsten Gehrke, Email: Thorsten.gehrke@helios-gesundheit.de.
Mustafa Citak, Email: Mustafa.citak@helios-gesundheit.de.
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