A biomechanical evaluation of press-fit stem constructs for tumor endoprosthetic reconstruction of the distal femur

Optimized reamer geometry for controlled reaming of the proximal femur

Preparation of the femoral proximal medullary cavity by reaming is essential for intramedullary nail osteosynthesis and hip revision arthroplasty. The use of reamers sometimes exerts high torsional forces on the bone. Design and direction of rotation of the reamer are potential influencing factors. The aim of this biomechanical study is to evaluate the best combination of a right- or left-cutting reamer with a clockwise- or counterclockwise-rotating insert in terms of preparation and safety. Right- and left-cutting reamers with conical design were each introduced into five synthetic femurs in both clockwise and counterclockwise rotation with constant feed force. A specially constructed test system was used for this series of tests, with which the respective intramedullary channel were reamed step by step. This was then used to determine the required torque. In addition, the feed rate measurement was analyzed using a modified digital caliper. The feed rates of the reamers with rotation in the same direction as the cutting direction were significantly increased compared to rotation in the opposite cutting direction (CCRLC vs. CCRRC 76.8 ± 9.0 mm/s vs. 25.2 ± 8.3 mm/s and CRRC vs. CRLC 54.3 ± 12.3 mm/s vs. 19.3 ± 0.6 mm/s; p < 0.01). In contrast, the mean torque during the reaming process was identical in all four groups. When preparing the proximal femoral medullary cavity, especially in cases with fragile bone structure, the available reamers should be introduced in opposite rotation to the cutting direction to achieve a more controllable feed of the reamer. Left-cutting reamers represent an alternative, using them in the usual clockwise-rotating technique to reduce the risk of complications during reaming.

Short-term clinical outcomes of Kyocera Modular Limb Salvage System designed cementless stems for the endoprosthetic reconstruction of lower extremities: a Japanese Musculoskeletal Oncology Group multi-institutional study

BACKGROUND

The high rate of aseptic loosening of cemented stems has led to their frequent use in endoprosthetic reconstruction. However, problems, such as stem breakage and stress shielding at the insertion site, remain. The Japanese Musculoskeletal Oncology Group (JMOG) has developed Kyocera Modular Limb Salvage System (KMLS) cementless stems with a unique tapered press-fit and short fixation design. This study aimed to clarify the short-term postoperative outcomes of this prosthesis and validate the stem design.

METHODS

One hundred cases of KMLS cementless stems (51 male patients; median age, 49 years; mean follow-up period, 35 months), with a minimum follow-up of 2 years, for the proximal femur (PF), distal femur (DF), and proximal tibia were prospectively registered for use. Prosthesis survival, complication rates, postoperative functional, and radiographical evaluation were analyzed. Complications or failures after insertion of the KMLS endoprostheses were classified into five types and functional results were analyzed according to the MSTS scoring system at postoperative 1 year. The diaphyseal interface and anchorage were graded by the ISOLS system at postoperative 2 years.

RESULTS

The overall prosthesis survival rates at 2 and 4 years were 88.2 and 79.6%, respectively. The prosthesis-specific survival rate excluding infection and tumor recurrence was 90.2 and 87.9%, respectively. Younger age (p = 0.045) and primary tumor (p = 0.057) were associated with poor prognosis of prosthesis-specific survival excluding infection and tumor recurrence. Complications were observed in 31 patients, 13 patients underwent revision surgery. The mean MSTS functional score at 1 year postoperatively was 68%. Early implant loosening was significantly more common in the DF (p = 0.006) and PF/DF straight stem (p = 0.038). The ISOLS radiographic evaluation at 2 years after surgery revealed good bone remodeling and anchorage in most cases (bone remodeling: 90% / excellent and good, anchorage: 97% / excellent and good).

CONCLUSIONS

Tumor endoprosthesis long-term fixation to the diaphysis of the lower extremity remains challenging. The KMLS cementless stem with a unique tapered press fit design showed good short-term results in maintaining bone stock. To prevent early loosening, a curved stem should be used in PF and DF, but long-term follow-up is necessary.

Distal femoral replacement - Cemented or cementless? Current concepts and review of the literature

Distal femoral endoprosthetic replacement has been successfully used to reconstruct distal femoral defects after tumor resection for over four decades. Despite continued advances, aseptic loosening continues to be the most common failure mode after infection. Debate still exists about a variety of design features and the optimal fixation method remains controversial. To date, no large-scale study or meta-analysis has demonstrated the superiority of one fixation technique over another. While the classic dichotomy of cemented versus cementless stems is well-known, the contemporary surgeon needs to fully understand the optimal clinical setting for each type of fixation technique and additional strategies to maximize implant stability. In clinical practice, the choice of fixation must be tailored to the individual patient. The surgeon must consider whether the operation is being performed for primary sarcoma or metastatic carcinoma, the presence of distant metastases, age, comorbidities, and whether radiotherapy has been previously given or will be required at the site of fixation. The best strategy for each patient optimizes tumor control and appropriately weighs risks of fixation failure versus the expected patient survival. This review will explore cemented and uncemented distal femoral replacement and highlight modern concepts to optimize each technique.

Biomechanical properties and thermal characteristics of frozen versus thawed whole bone

Biomechanics research often requires cadaveric whole bones to be stored in a freezer and then thawed prior to use; however, the literature shows a variety of practices for thawing. Consequently, this is the first study to report the mechanical properties of fully frozen versus fully thawed whole bone as 'proof of principle'. Two groups of 10 porcine ribs each were statistically equivalent at baseline in length, cross-sectional area, and bone mineral density. The two groups were stored in a freezer for at least 24 h, thawed in air at 23 °C for 4 h while temperature readings were taken to establish the time needed for thawing, and once again returned to the freezer for at least 24 h. Mechanical tests to failure using three-point bending were then done on the 'frozen' group immediately after removal from the freezer and the 'thawed' group when steady-state ambient air temperature was reached. Temperature readings over the entire thawing period were described by the line-of-best-fit formula T = (28.34t - 6.69)/(t + 0.38), where T = temperature in degree Celsius and t = time in hours, such that frozen specimens at t = 0 h had a temperature of -17 °C and thawed specimens at t = 1.75 h reached a steady-state temperature of 20 °C-23 °C. Mechanical tests showed that frozen versus thawed specimens had an average of 32% higher stiffness k, 34% higher ultimate force F_u, 28% lower ultimate displacement δ_u, 40% lower ultimate work W_u, 43% higher elastic modulus E, 37% higher ultimate normal stress σ_u, and 33% higher ultimate shear stress τ_u. Whole ribs failed at midspan primarily by transverse cracking (16 of 20 cases), oblique cracking (three of 20 cases), or surface denting (one of 20 cases), each having unique shapes for force versus displacement graphs differentiated mainly by ultimate force location.

Midterm Success of a Custom, Non-Fluted, Diaphyseal, Press-Fit Stem Used With a Tumor Megaprosthesis System

BACKGROUND

High rates of aseptic loosening with cemented prostheses have led to increased utilization of uncemented stems in the setting of megaprosthetic reconstruction. Theoretic concerns of rotational instability resulted in early stem designs with de-rotational mechanisms such as flutes or side plates. However, these designs have their own associated complications, and mechanical data suggest they are unnecessary. The purpose of this study is to evaluate outcomes and survivorship of an unfluted diaphyseal press-fit stem in the setting of megaprosthetic reconstruction.

METHODS

Forty-five patients (46 stems), with a minimum 3-year follow-up, underwent reconstruction using 1 of 2 fully porous coated, unfluted, press-fit stems between 2005 and 2013: revision stem with adapter to the megaprosthesis (revision stem), or custom megaprosthesis stem (custom stem). Complications were described using the Henderson classification system, and subanalyses evaluated stem-related failures and survival. Radiographic evaluation of stem fixation was determined via evidence of bone bridging, spot welding, resorption, subsidence, and pedestal formation. Four patients had early stem removal for local recurrence or infection and were thus excluded from the radiographic analyses.

RESULTS

Twenty-eight femoral (15 revision stem, 13 custom stem) and 14 tibial (6 revision stem, 8 custom stem) stems were reviewed. Average follow-up was 81 months (range, 42-140 months). Revision for implant-related complications occurred in 7 of 41 (17%), all in revision stems (3 adapter failures, 4 polyethylene wear). At final follow-up, all stems were retained without evidence of aseptic loosening, although 7 of 41 (17%) exhibited mild stress shielding.

CONCLUSION

A non-fluted, press-fit stem used with a tumor prosthesis provided a stable bone-prosthesis interface at midterm follow-up.

Fixed-hinge cemented modular implants: An effective reconstruction technique following primary distal femoral bone tumor resection. A 136-case multicenter series

BACKGROUND

Reconstruction by endoprosthesis is widespread after bone tumor resection. The design and type of fixation and of hinge remain a matter of debate. The aim of the present study was to assess survival, complications and functional results in a homogeneous series of adult patients undergoing bone defect reconstruction following distal femoral tumor resection, using a single model of fixed-hinge cemented endoprosthesis, at a minimum 5 years' follow-up.

HYPOTHESIS

The study hypotheses were that loosening and infection are the main causes of failure, and that this type of reconstruction is reliable following distal femoral resection.

PATIENTS AND METHODS

All patients aged over 17 years undergoing reconstruction using the Stanmore Mets® fixed-hinge cemented modular endoprosthesis following distal femoral resection for primary bone tumor in 4 French reference centers between 2004 and 2013 were included. Epidemiological data, MSTS functional score, clinical and radiological examination results, complications and survival with types of failure according to the Henderson classification were assessed.

RESULTS

One hundred and thirty-six patients (68 male, 68 female; mean age, 41.2 years [range, 17-77 years]) were included. Mean follow-up was 81 months [range, 61-134 months]. Thirty-two patients (38%) experienced a total 67 complications requiring surgical revision: mainly infection (n=28) or mechanical failure (n=26). Overall implant survival was 78% at 5 years. There were 30 implant failures on the Henderson classification. Mean MSTS score was 82%.

DISCUSSION

The present results are comparable to those of the literature and for other types of reconstruction. Recent meta-analyses suggest that type of hinge and of stem fixation have little effect on implant survival. International comparative studies are needed to determine the exact role of each type of reconstruction according to the patient profile.

LEVEL OF EVIDENCE

IV, multicenter retrospective series.

Osteointegration in Compliant Self-Adjusting Compression Fixation Shown by Backscatter Electron Microscopy: A Case Report

Compliant self-adjusting compression implants are a novel approach to increase the durability of megaprosthesis fixation. However, there is no report of current implant designs that documents the bone-prosthetic interface of this implant. A well-fixed compliant, self-adjusting distal femoral replacement was retrieved from a patient undergoing revision unrelated to fixation. The prosthesis-bone interface was preserved, embedded in poly(methyl methacrylate), and sectioned into 2-4-mm slices. Slices were then imaged using backscatter electron microscopy, and ongrowth and ingrowth were quantified using imaging software. The average percentage of bony ongrowth from five successive sections was 52.5%, and the average percentage of ingrowth into the porous titanium surface was 13.5%. We found that bone ongrowth on the cortex between anchor plug and spindle averages more than 50% and up to 70% depending upon the slice examined with backscatter electron microscopy. Bone ingrowth was consistently around 13% on every slice examined. This is a new finding compared with prior spindle designs, likely due to the addition of hydroxyapatite-coated porous metal titanium surface on the spindle. This report is an important step in understanding the mechanism of bony fixation generated by this implant and supports its increased use in oncological and complex reconstructive situations.

Anchoring of a Kinked Uncemented Femoral Stem after Preparation with a Straight or a Kinked Reamer

Objective

To investigate a stem‐adjusted preparation of the femur with a kinked reamer and to determine whether this approach results in higher primary stability of a kinked stem than straight reaming of the intramedullary canal.

Methods

Ten cementless stems with a kinked design were implanted in synthetic femurs after preparation of the femoral canal with 2 different reamer designs (straight reaming [SR] group vs kinked reaming [KR] group). The specimens were analyzed using CT to determine the anchoring length and examined with a mechanical testing system to establish their axial stiffness, torsional stiffness, and migration distance after 10 000 gait cycles.

Results

The stem migration distances did not differ significantly between the groups (SR group 0.51 ± 0.16 mm vs KR group 0.36 ± 0.03 mm, P = 0.095). Only for the SR group, a correlation was found between the completely conical anchorage length and absolute stem migration (P < 0.05, R = 0.89). Regarding the torsional stiffness, no differences were observed between the study groups (SR group 6.48 ± 0.17 Nm/° vs KR group 6.52 ± 0.25 Nm/°, P = 0.398). In the KR group, significantly higher axial stiffness values were measured than in the SR group (SR group 1.68 ± 0.14 kN/mm vs KR group 2.09 ± 0.13 kN/mm, P = 0.008).

Conclusions

The implantation of a kinked stem after kinked conical intramedullary preparation of the proximal femur showed equivalent results regarding anchoring length, stem migration, and torsional stiffness to those for straight conical reaming. The specimens with kinked reaming showed significantly higher axial stiffness values.

The Proximal and Distal Femoral Canal Geometry Influences Cementless Stem Anchorage and Revision Hip and Knee Implant Stability

Although cementless revision arthroplasty of the hip has become the gold standard, revision arthroplasty of the distal femur is controversial. This study evaluated the anchoring principles of different femoral revision stem designs in extended bone defect situations, taking into account the anatomical conditions of the proximal and distal femur, and the resulting primary stability. Cementless press-fit stems of 4 different designs were implanted in synthetic femurs. The specimens were analyzed by computed tomography and were tested considering axial/torsional stiffness and migration resistance. Different stem designs anchored in different femoral canal geometries achieved comparable primary stability. Despite considerably different anchorage lengths, no difference in migration behavior or stiffness was found. Both in the distal femur and in the proximal femur, the conical stems showed a combination of conical and 3-point anchorage. Regarding the cylindrical stem tested, a much shorter anchorage length was sufficient in the distal femur to achieve comparable primary stability. In the investigated osseous defect model, the stem design (conical vs cylindrical), not the geometry of the femoral canal (proximal vs distal), was decisive regarding the circumferential anchorage length. For the conical stems, it can be postulated that there are reserves available for achieving a conical-circular fixation as a result of the large contact length. For the cylindrical stems, only a small reserve for a stable anchorage can be assumed. [Orthopedics. 2018; 41(3):e369-e375.].

Early follow-up of a custom non-fluted diaphyseal press-fit tumour prosthesis

PURPOSE

The objective of this study was to evaluate the early results of a custom non-fluted diaphyseal press-fit stem for use with the global modular replacement system (GMRS) tumour prosthesis and the early complications associated with this implant.

METHODS

A total of 53 patients (54 implants) were identified from a prospective database where a custom non-fluted diaphyseal press-fit stem was used as part of the reconstruction of the limb. All patients had a minimum of 22 months of follow-up.

RESULTS

The rates of stem revision for any reason were calculated. The median follow-up was 36 months (range 22-85 months). Aseptic loosening was not observed in any patient.

CONCLUSIONS

At early term follow-up, an uncemented non-fluted stem used with the GMRS tumour endoprosthesis provides a stable bone-prosthesis interface with no evidence of aseptic loosening.

A biomechanical comparison of four different cementless press-fit stems used in revision surgery for total knee replacements

Few biomechanical studies exist on femoral cementless press-fit stems for revision total knee replacement (TKR) surgeries. The aim of this study was to compare the mechanical quality of the femur-stem interface for a series of commercially available press-fit stems, because this interface may be a 'weak link' which could fail earlier than the femur-TKR bond itself. Also, the femur-stem interface may become particularly critical if distal femur bone degeneration, which may necessitate or follow revision TKR, ever weakens the femur-TKR bond itself. The authors implanted five synthetic femurs each with a Sigma Short Stem (SSS), Sigma Long Stem (SLS), Genesis II Short Stem (GSS), or Genesis II Long Stem (GLS). Axial stiffness, lateral stiffness, 'offset load' torsional stiffness, and 'offset load' torsional strength were measured with a mechanical testing system using displacement control. Axial (range = 1047-1461 N/mm, p = 0.106), lateral (range = 415-462 N/mm, p = 0.297), and torsional (range = 115-139 N/mm, p > 0.055) stiffnesses were not different between groups. The SSS had higher torsional strength (863 N) than the other stems (range = 167-197 N, p < 0.001). Torsional failure occurred by femoral 'spin' around the stem's long axis. There was poor linear correlation between the femur-stem interface area versus axial stiffness (R = 0.38) and torsional stiffness (R = 0.38), and there was a moderate linear correlation versus torsional strength (R = 0.55). Yet, there was a high inverse linear correlation between interfacial surface area versus lateral stiffness (R = 0.79), although this did not result in a statistical difference between stem groups (p = 0.297). These press-fit stems provide equivalent stability, except that the SSS has greater torsional strength.

The biomechanics of three different fracture fixation implants for distal femur repair in the presence of a tumor-like defect

The femur is the most common long bone involved in metastatic disease. There is consensus about treating diaphyseal and epiphyseal metastatic lesions. However, the choice of device for optimal fixation for distal femur metaphyseal metastatic lesion remains unclear. This study compared the mechanical stiffness and strength of three different fixation methods. In 15 synthetic femurs, a spherical tumor-like defect was created in the lateral metaphyseal region, occupying 50% of the circumference of the bone. The defect was filled with bone cement and fixed with one of three methods: Group 1 (retrograde nail), Group 2 (lateral locking plate), and Group 3 (lateral nonlocking periarticular plate). Constructs were tested for mechanical stiffness and strength. There were no differences between groups for axial stiffness (Group 1, 1280 ± 112 N/mm; Group 2, 1422 ± 117 N/mm; and Group 3, 1403 ± 122 N/mm; p = 0.157) and offset torsional strength (Group 1, 1696 ± 628 N; Group 2, 1771 ± 290 N; and Group 3, 1599 ± 253 N; p = 0.816). In the coronal plane, Group 2 (296 ± 17 N/mm) had a higher stiffness than Group 1 (263 ± 17 N/mm; p = 0.018). In the sagittal plane, Group 1 (315 ± 9 N/mm) had a higher stiffness than Group 3 (285 ± 19 N/mm; p = 0.028). For offset torsional stiffness, Group 1 (256 ± 23 N/mm) had a higher value than Group 3 (218 ± 16 N/mm; p = 0.038). Group 1 had equivalent performance to both plating groups in two test modes, and it was superior to Group 3 in two other test modes. Since a retrograde nail (i.e. Group 1) would require less soft-tissue stripping in a clinical context, it may be the optimal choice for tumor-like defects in the distal femur.