The saddle prosthesis initially was designed for reconstruction of large acetabular defects in revision hip arthroplasty, but it has been used primarily for hip reconstruction after periacetabular tumor resections. For periacetabular reconstruction with the saddle prosthesis a notch is created in the iliac remnant [23
], and in the event of large resections the remaining iliac wing can be augmented additionally with a cortical allograft to create a more stable notch. The saddle articulates with the iliac notch and does not require an exact anatomic fit. The saddle design has no formal constraint, but does have four modular interpositional components to build an optimal offset and length for soft tissue tensioning. The goals of surgical treatment of periacetabular tumors are wide resection providing local control and optimal chance for survival, preservation of limb function, and quality of life. Previous reports have been published on the surgical and functional outcomes of saddle prostheses [1
], but functional outcome in long-term survivors with these reconstructions remains unclear. Therefore we examined the long-term functional results and complications in patients treated with a saddle prosthesis after periacetabular tumor resection.
We recognize some limitations to our study. First, it is a retrospective case series, which makes comparison with a concurrent control group impossible. Therefore the exact influence of the extensive exposure needed for excision of periacetabular tumors with safe margins remains unclear. Second, the group of long-term survivors is relatively small and functional scoring has not been documented on an annual basis for all patients. Third, the operative time was not documented for all patients, therefore, it is not clear whether surgical technique or a learning curve could have influenced the high rate of complications. Fourth, only 17 patients have undergone surgery during a 16-year period. Although the operation rate was approximately one saddle prosthesis per year, the senior surgeons had extensive experience in this surgical field with different types of orthopaedic oncology surgery and arthroplasty during this period. The Leiden University Medical Centre has been a national referral center for orthopaedic oncology for more than 25 years. In the same 5-year period as in this study 24 pelvic reconstructions of other types were performed after periacetabular Stages P1 through 3 tumor resections. Compared with other studies the mean length of surgery also was shorter (Table ). For these reasons we believe the limited number of procedures did not influence the complication rate.
Literature comparison of long-term functional outcome of saddle protheses
In comparison to previous short-term followup series, the mean followup of 12.1 years in our study (with minimal followup of 8.3 years) of the surviving patients for whom functional scores with TESS and MSTS were measured, is substantially longer. Cottias et al. [8
] reported a series of patients with a mean followup of 42 months. Functional scoring for nine patients showed a mean MSTS score of 57% and a mean TESS score of 58%. Kitagawa et al. [20
] reported functional scores for a group of seven patients with a mean followup of 21 months. They reported a mean MSTS score of 45% for the seven patients, and six patients had a mean TESS score of 61%. Aljassir et al. [2
] had a group of 16 patients with mean followup of 45 months, a mean MSTS score of 51%, and mean TESS score of 64%. Renard et al. [25
] measured functional outcome at 1 and 2 years after a saddle prosthesis in 11 and six surviving patients respectively, and reported mean MSTS scores of 53% and 51%. Aboulafia et al. [1
] described the results of patients treated with saddle prostheses by a grading system depending on oncologic outcome, ambulatory function, and use of pain medication. Of the nine patients still alive after an average of 33 months, the overall results were reported as “excellent” in seven patients and “good” in two patients. The functional outcome scores for our patients with long-term followup are slightly less (mean MSTS score, 47%; mean TESS score, 53%) than reported by other authors with substantially shorter followups. The functional results after pelvic reconstruction with the saddle prosthesis, and especially the poor hip flexion, are related to the eccentric position of the new rotational center of the hip that allows only limited ROM [29
]. However, the extended resection has a negative effect on patient function [3
Major complications after periacetabular reconstructions are common (ranging from 33%–65%) and can be related to the surgical procedure, tumor extension, the implant, and comorbidities of the patient [1
]. The type and incidence of complications after saddle prosthesis reconstruction in our patients are comparable to those reported by others. Wound complications, occurring in 18% to 37% of patients [1
], are wound dehiscence, skin necrosis, and superficial and deep infections. Risk factors for the high incidence of wound problems are the long operating time, large surgical exposure, high volume of blood loss, lack of muscular and soft tissue coverage, large dead space after resection, and the patients’ immune system compromised by chemotherapy and radiotherapy. Reported neurologic complications are transient peroneal nerve paresis and neurapraxia of the sciatic and femoral nerves attributable to manipulation of the femur. The bony complications that frequently are described are fractures of the remaining iliac wing and proximal migration of the saddle component (range, 0%–7%), which causes leg length difference and dislocations (range, 0%–18%) [1
]. When large resection of the iliac wing is required, more proximal migration has been reported [1
]. In cases where continuous cranial migration of the saddle prosthesis is observed (Fig. ), the patient is likely to have a deep wound infection [23
]. We used nonresorbable sutures around the iliac wing and the saddle to prevent dislocation, and bone grafting of the iliac notch was used in case of a narrow remnant iliac wing, as described by others [8
]. Heterotopic ossifications can be seen growing from the iliac remnant several months postoperatively, which can have a negative effect on functional outcome. Oncologic complications are local recurrence and systemic progressive disease [16
Fig. 2A–B This patient had a periacetabular osteosarcoma induced by radiotherapy, for which a Type 2 internal hemipelvectomy was performed, with pelvic reconstruction using the saddle prosthesis. (A) AP and (B) lateral view radiographs obtained 6 years (more ...)
The Mark II saddle prosthesis (Link, Hamburg, Germany) used in our series is a second-generation design that offers better mobility and stability because of its modular design compared with the first-generation nonmodular Mark I design [23
]. It still requires additional bone resection to create an iliac notch and provides an unstable articulation causing a high risk of mechanical failure at the ilium-to-saddle interface. Furthermore, the postoperative function based on the MSTS and TESS scores of the patients after saddle prosthesis reconstruction was not superior to other reconstructions with pelvic prostheses, allograft reconstruction, arthrodesis, or pseudarthrosis [20
]. To address the mechanical complications of the saddle prosthesis, the periacetabular reconstruction (PAR) endoprosthesis was developed, which is a third-generation modular design consisting of an iliac wing component fixed to the ilium with screws and cement [15
]. The modular femoral stem articulates with a constrained socket joint, which is embedded in the iliac wing component. Menendez et al. [21
] reported results for 25 patients treated with the PAR endoprosthesis with a mean followup of 29 months and an average MSTS score of 67%. Although this third-generation saddle design did provide some functional improvement, major complications still occurred in 56% of the patients and implant survivorship after 5 years was reported at 60% [21
]. In the study by Menendez et al. [21
], 14 of 25 patients had at least one major complication: there were eight infections, five reoccurrences, three dislocations, two fractures, one malposition, one necrosis, and one heterotopic ossification.
Some authors prefer pelvic reconstruction by pseudarthrosis [16
] instead of reconstruction with allografts [24
] or an endoprosthesis [30
], because of difficulty in providing a firm long-lasting reconstruction and high complication rates. However, in addition to limited motion and inconvenient leg length discrepancy, failure of fusion often occurs, resulting in a painful pseudarthrosis with unsatisfactory functional outcome [7
To improve outcome after reconstruction of large defects after periacetabular resection new custom implants and ball and socket-type implants with pedestal-based cups have been developed. These newer types of tumor prostheses consist of a socket with a cone-shaped pedestal attached, which is inserted into the remaining iliac body toward the superior border of the sacroiliac joint for stable fixation. Some designs offer a modular cup for restoration of anatomic inclination and anteversion, which articulates with a large ceramic or tripolar head potentially offering more stability. Because no iliac notch has to be created less bone resection and soft tissue exposure is required, but complications otherwise related to the challenges of periacetabular tumor resections probably will remain unchanged. Although these new pedestal-based designs theoretically may offer improved function, no long-term followup data are available yet.
Reconstruction with saddle prostheses after periacetabular tumor surgery has a high risk of complications and poor long-term functional outcome with limited hip flexion. Based on our study with limited patient numbers but long-term followup the saddle prosthesis cannot be recommended for pelvic reconstruction after internal hemipelvectomy. Therefore in our center we no longer use the saddle prosthesis for reconstruction after periacetabular tumor resections. New more anatomic modular designs for pelvic reconstruction may offer better stability and mobility with cone-shaped, pedestal-based designs, but long-term followup is required to assess survivorship and functional outcome.