Osteoporosis and anterior femoral notching in periprosthetic supracondylar femoral fractures: a biomechanical analysis

Total knee arthroplasty and periprosthetic distal femoral fracture: looking beyond the osteoporosis to previous osteoporotic fracture

Osteoporosis increases the risk of periprosthetic distal femoral fractures after TKA, especially in patients with a history of osteoporotic fractures. Therefore, careful assessment and proper treatment of osteoporosis need and the importance of taking osteoporotic medication needs to be recognized by the patients following primary TKA.

PURPOSE

Osteoporosis is a risk factor for fractures, including those of the hip, vertebrae, and distal radius; however, the association between osteoporosis and periprosthetic fractures after total knee arthroplasty (TKA) has not been much investigated. Therefore, we aimed to investigate the association of the presence of systemic osteoporosis with periprosthetic fractures after TKA.

METHODS

This study included 34 patients with periprosthetic fractures following primary TKA and 106 controls matched for age and sex. Bone mineral density was evaluated at the femoral neck, total hip, and lumbar spine using dual X-ray absorptiometry. Medical records were reviewed for age; sex; body mass index; smoking; rheumatoid arthritis, endocrine diseases, and cardiovascular diseases; history of glucocorticoid use; medication for osteoporosis; and history of previous osteoporotic fracture. In addition, anterior femoral notching after TKA was evaluated. Univariable and multivariable logistic regression analysis were used to determine factors associated with periprosthetic fracture.

RESULTS

The prevalence of osteoporosis in the fracture group was higher than that in the control group (61.8% vs. 40.6%, p=0.045). The rate of medication for osteoporosis was significantly low in the fracture group (47.6 % vs 76.7%, p=0.026). History of previous osteoporotic fracture (odds ratio [OR], 9.1; p=0.015) and osteoporosis (OR, 3.6; p=0.013) were significant risk factors for periprosthetic fractures after TKA. Medication for osteoporosis could decrease the risk of periprosthetic fracture (OR 0.3; p=0.020).

CONCLUSION

Osteoporosis is a major risk factor for periprosthetic distal femoral fractures after TKA. Therefore, careful assessment and proper treatment of osteoporosis need and the importance of taking osteoporotic medication needs to be recognized to the patients following primary TKA, especially in patients with a history of osteoporotic fracture.

LEVEL OF EVIDENCE

Prognostic study, level III.

Discrepancies in Sagittal Alignment of the Lower Extremity Among Different Brands of Robotic Total Knee Arthroplasty Systems

BACKGROUND

There is an increasing number of different brands of robotic total knee arthroplasty (TKA) systems. Most robotic TKA systems share the same coronal alignment, while the definitions of sagittal alignment vary. The purpose of this study was to investigate whether these discrepancies impact the sagittal alignment of the lower extremity.

METHODS

A total of 72 lower extremity computed tomography scans were included in our study, and 3-dimensional models were obtained using software. A total of 7 brands of robotic TKA systems were included in the study. The lower extremity axes were defined based on the surgical guide for each implant. We also set the intramedullary axis as a reference to evaluate the discrepancies in sagittal alignment of each brand of robotic system.

RESULTS

On the femoral side, the axis definition was the same for all 7 robotic TKA systems. The robotic TKA axes showed a 2.41° (1.58°, 3.38°) deviation from the intramedullary axis. On the tibial side, the 7 robots had different axis definitions. The tibial mechanical axis of 6 of the TKA systems was more flexed than that of the intramedullary axis, which means the posterior tibial slope was decreased while the tibial mechanical axis of the remaining system was more extended.

CONCLUSIONS

The sagittal alignment of the lower extremity for 7 different brands of robotic TKA systems differed from each other and all deviated from the intramedullary axis. Surgeons should be aware of this discrepancy when using different brands of robotic TKA systems to avoid unexpected sagittal alignment and corresponding adverse clinical outcomes.

LEVEL OF EVIDENCE

Level IV, Therapeutic Study.

Robotic-assisted total knee arthroplasty results in decreased incidence of anterior femoral notching compared to posterior referenced instrumented total knee arthroplasty

OBJECTIVE

Periprosthetic fracture (PPF) is an uncommon but devastating complication after total knee arthroplasty (TKA). Anterior femoral notching (AFN) is one of a perioperative risk factor for PPF. The main purpose of this study was to compare between the rates of anterior femoral notching (AFN) and supracondylar periprosthetic femoral fracture (sPPF) of manual TKA and robotic arm-assisted TKA (RATKA). Meanwhile, blood loss, transfusion rates, inflammatory responses, complications, early clinical and radiological outcomes were also assessed.

METHODS

This retrospective study included 330 patients (133 RATKA and 197 manual TKA). Differences in risks of inflammatory, blood loss, complications (periprosthetic fracture and periprosthetic joint infection), pre-operative and post-operative distal lateral femoral angle (LDFA), distal femoral width (DFW), prosthesis-distal femoral width (PDFW) ratio, AFN, femoral component flexion angle (FCFA), peri-operative and post-operative functional outcomes between the RATKA and manual TKA groups were compared.

RESULTS

The operation time and postoperative CRP level in the RATKA group was significantly longer and higher than that in the manual TKA group (p < .001). However, there was no significant difference in postoperative WBC level (p = .217), hemoglobin loss (p = .362), postoperative drainage (p = .836), and periprosthetic fracture (p = 1.000). There was no significant difference in LDFA (p > .05), DFW(p = .834), PDFW ratio (p = .089) and FCFA (p = .315) between the two groups, but the rate of AFN in the RATKA group was significantly lower than that in the manual TKA group (p < .05). There was no significant difference in ROM between the two groups on POD3, POD 90 and 1 year (p < .05), but the FJS-12 score in the RATKA group was higher than that in the manual TKA group on 1 year (p = .001).

CONCLUSION

Robotic-assisted total knee arthroplasty can decrease the incidence of anterior femoral notching compared to posterior referenced instrumented total knee arthroplasty.

Combined nail-plate constructs in the management of osteoporotic native distal femoral fractures: a systematic review of the available evidence

PURPOSE

Distal femoral fractures account for 4-6% of fragility fractures. These may be managed using a combined nail-plate construct (NPC). The use of NPCs is gaining traction. Whilst several theoretical advantages exist, there is little evidence reporting on binary or patient-reported outcomes. The aim of the current study was to perform a systematic review of the available literature pertaining to NPCs and their treatment of native distal femoral fractures, appraising the outcomes and focusing on the rationale for their increasing uptake in recent literature.

METHODS

A comprehensive search of MEDLINE, EMBASE, Clinical Key, PubMed and Cochrane library was performed from date of inception up to in August 9, 2022. All study languages were included initially. A further Google Scholar search review was performed to identify any other studies not identified in the database interrogation. Studies were eligible if they reported on the use of nail-plate constructs in managing distal femoral fractures. Any outcome metric was permitted. The study was conducted in accordance with PRISMA guidelines. Risk of bias was assessed using the Methodological Index for non-randomised Studies tool. Quantitative analysis was performed using a log odds ratio random effects model. The Knapp-Hartung adjustment was utilised if the total number of included studies was < 5. Study effect sizes and appropriate plots were constructed to illustrate the outcomes data.

RESULTS

A total of four studies were eligible for inclusion. Study data was extracted and summarised with their relevant outcomes presented. The literature review demonstrated that the use of NPCs led to significantly earlier full weight bearing (p < 0.001) and had reduced non-union rates over a single construct, without affecting infection rates (12.5% vs. 5.6%; p = 0.289) and significantly lower implant failure rates (10.5% vs. 0%; p = 0.011). A meta-analysis is performed of available studies and Forrest plots presented.

CONCLUSION

The use of NPC in the management of native osteoporotic DFFs is gaining traction but the available evidence is of low grade with significant heterogeneity in small cohorts of patients. We suggest that a large-scale, multicentre prospective study should be performed, with agreed functional and radiological outcome metrics, to provide a more robust evidence base.

Sagittal Alignment in Total Knee Arthroplasty: Are There Any Discrepancies Between Robotic-Assisted and Manual Axis Orientation?

BACKGROUND

Sagittal alignment determines the extension and flexion of knee prostheses in total knee arthroplasty (TKA). The definition of the sagittal axes may be different between the Mako TKA system (Stryker) and the conventional manual intramedullary approach. Whether there is any discrepancy between the 2 approaches has not been well studied.

METHODS

We retrospectively analyzed 60 full-length computed tomographic (CT) scans of the lower extremities of 54 patients. The femur and tibia were modeled by using Mimics (Materialise). The Mako mechanical axes were determined according to the Mako TKA Surgical Guide. The manual intramedullary axes were determined according to the central axis of the tibial proximal and femoral distal medullary cavities. The femoral, tibial, and combined angular discrepancies were measured in the sagittal plane.

RESULTS

On the femoral side, the Mako mechanical axis was more likely to be located in an extended position relative to the manual intramedullary axis (56 of 60 knees). The median angular discrepancy was 2.46° (interquartile range [IQR], 1.56° to 3.43° [range, -1.06° to 5.24°]). On the tibial side, the Mako mechanical axis was likely to be located in a flexed position relative to the manual intramedullary axis (57 of 60 knees). The median angular discrepancy was 2.40° (IQR, 1.87° to 2.84° [range, -0.79° to 4.20°]). The angular discrepancy of the femoral-tibial sagittal angle was 4.63° (IQR, 3.71° to 5.64° [range, 1.20° to 9.02°]).

CONCLUSIONS

Compared with manual TKA, the Mako system is more likely to result in a decreased posterior tibial slope and extension of the femoral prosthesis. It may also influence the evaluation of lower-extremity extension and flexion. When using the Mako system, special attention should be given to these discrepancies.

LEVEL OF EVIDENCE

Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

The Role of Stability and Alignment in Improving Patient Outcomes After Total Knee Arthroplasty

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Total knee arthroplasty (TKA) is an effective treatment option for many patients, but a small group of patients are dissatisfied following TKA.

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Alignment, in combination with balance, stability, and knee kinematics, is an important modifiable surgical factor that can affect patient outcomes.

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Driven by the subset of dissatisfied patients after TKA, new techniques have evolved in the search for a more anatomic reconstruction of individual knee morphology and a more accurate approximation of the individual lower-extremity alignment.

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There is a need to optimize 3 aspects of TKA to improve patient outcomes-mechanical tooling processes, implants that resurface the epiphysis, and techniques that respect the variable anatomy of patients.

Is the femoral component flexion affected by the sagittal femoral shaft bowing in conventional intramedullary guided TKA?

BACKGROUND

The aim of the present study was to investigate the influence of sagittal femoral bowing on sagittal femoral component alignment, and whether there was correlation between sagittal femoral component alignment and coronal femoral component alignment.

METHODS

We retrospectively reviewed 77 knees in 71 patients who had undergone primary TKA for advanced osteoarthritis. All surgeries were performed by using a standard medial parapatellar approach. The osteotomy was performed with a conventional technique using an intramedullary rod for the femur and a mechanical extramedullary guiding system for the tibia. All patients enrolled in the study were evaluated with full-length lower extremity load-bearing standing scanograms, and the patients had preoperative and postoperative radiographs of the knees. Coronal femoral bowing angle (cFBA), sagittal femoral bowing angle (sFBA), and postoperatively, mechanical tibiofemoral angle of the knee (mTFA), β angle (femoral component flexion angle) were measured. The radiographic results of both groups were compared using Student's t test. A two-sided Pearson correlation coefficient was obtained to identify the correlations between FBA in the coronal and sagittal planes, as well as FBA and age or BMI, sFBA and β angle, cFBA and mTFA. Comparison of FSB incidence between different genders was made using Chi-square test. The p value < 0.05 indicates a statistically significant difference.

RESULTS

The mean sFBA, cFBA, β angle, mTFA were 9.34° ± 3.56°(range 1°-16°), 3.25° ± 3.79°(range - 7° to -17°), 3.91° ± 3.15°(range - 1° to -13°), 0.60° ± 1.95°(range - 3° to -6°), respectively. There was no correlation between age and sFBA (CC = 0.192, p = 0.194) or cFBA (CC = 0.192, p = 0.194); similarly, there was no correlation between age and sFBA (CC = 0.067, p = 0.565) or cFBA (CC = 0.069, p = 0.549). The sFBA was correlated with cFBA and β angle (CC = 0.540, p < 0.01; CC = 0.543, p < 0.01, respectively), and the cFBA was correlated with mTFA (CC = 0.430, p < 0.01). There was no significant difference (p = 0.247) of cFBA between the patients with sFSB and the patients without sFSB.

CONCLUSIONS

The current study showed that the sFBA was correlated with cFBA in the patients undergoing TKA and the patients with sFSB usually presented non-cFSB. We also found that sFSB could affect the femoral component alignment in the sagittal plane and cFSB could affect the femoral component alignment in the coronal plane. The sFBA or cFBA was not correlated with age, BMI, or gender.

[Research progress of anterior femoral notching in total knee arthroplasty]

Objective

To summarize the research progress of the causes and prevention methods of anterior femoral notching in total knee arthroplasty (TKA).

Methods

The related literature at home and abroad about the causes and prevention methods of the anterior femoral notching in TKA was extensively reviewed and summarized.

Results

The reasons for the occurrence of anterior femoral notching can be summarized as follows: the application of the posterior reference technique, the increase of the posterior condylar angle, the variant anatomical shape of anterior femoral cortex, the selective reduction of the femoral prosthesis size, backward movement of the entrance point, and the application of computer-assisted navigation technology or patient-specific instrumentation. To prevent the occurrence of anterior femoral notching, programs such as flex the femoral prosthesis, robot-assisted technology, and anterior and posterior reference techniques combination can be used.

Conclusion

Anterior femoral notching is a common surgical complication of TKA. A complete preoperative plan, assessment of the patient's knee joint condition, and development of a reasonable surgical plan can effectively reduce the occurrence of anterior femoral notching.

Treatment of B1 Distal Periprosthetic Femur Fractures

The burden of periprosthetic distal femoral fractures is projected to increase accordingly with the increase in total knee arthroplasties (TKAs) performed globally in the future. Less invasive plating and intramedullary (IM) nailing techniques still seem to provide similar outcomes based on current literature. Double-plating and combination techniques may prove to be beneficial in the future pending further large-scale studies but currently have not demonstrated superiority over single plating and IM nailing based on current evidence. Distal femoral replacement may provide a useful option for future treatment, provided it is performed by a trained knee arthroplasty surgeon.

Anterior femoral notching ≥ 3 mm is associated with increased risk for supracondylar periprosthetic femoral fracture after total knee arthroplasty: a systematic review and meta-analysis

PURPOSE

Anterior femoral notching (AFN) may be associated with a higher risk for supracondylar periprosthetic fracture (sPPF) after total knee arthroplasty (TKA), although studies have yielded inconclusive results. We aimed to systematically investigate and meta-analyze the best available evidence regarding the association between AFN and the risk of sPPF after TKA.

METHODS

A comprehensive search of PubMed, Scopus, Mendeley, Google Scholar and Cochrane databases was performed, from conception to February 29, 2020. Data were expressed as odds ratio (OR) with 95% confidence intervals (CI). I²-index was employed for heterogeneity. Newcastle-Ottawa scale was implemented for quality assessment of the included studies.

RESULTS

Nine studies fulfilled the eligibility criteria, including a total of 3264 patients subjected to TKA. Among them, there were 150 patients who sustained a sPPF. Overall, patients exposed to AFN (AFN group) demonstrated an increased risk for sPPF compared to those not exposed (control group) (OR 3.91, 95% CI 1.22-12.58, p = 0.02; I² 68.52%). Subgroup analysis based on AFN depth with a cut-off value of 3 mm further clarified this association. Patients with AFN ≥ 3mm were at higher risk for sPPF compared to patients with AFN < 3 mm and control group (OR 4.85, 95% CI 2.08-11.33, p = 0.00; I² 0.0%). On the contrary, fracture risk was not significant for patients with AFN < 3 mm compared to the control group (OR 5.0, 95% CI 0.44-56.82, p = 0.19; I² 42.99%).

CONCLUSION

Patients, exposed to AFN ≥ 3 mm in depth, are at higher risk for sustaining a sPPF.

Total knee arthroplasty with distal femoral replacement is associated with an important complication rate. A case series

BACKGROUND

With the aging population and an increasing number of total knee arthroplasties (TKAs) performed yearly worldwide, revision surgeries for many causes (septic or aseptic loosening, periprosthetic femoral fractures (PDFF), non-unions, malunions) are more frequent and challenging. Distal femoral replacement (DFR) is sometimes the only option to restore knee function and quality of life. DFR in non-oncologic patient is still a rare indication and few reports are published on this topic, with a non-consistent variety of functional results, complication rates and survivorship.

METHODS

We present a retrospective series of patients who underwent a DFR for a non-oncologic indication between 2010 and 2017. Nineteen patients were available for a full evaluation (clinical and radiological) with a mean follow-up of 48.3 months (range 15-99). Goniometry was performed at the six-week postoperative visit. Complications were reported. Osteolysis and/or signs of aseptic loosening were described using the Knee Society Radiographic Evaluation. Survivorship was calculated for aseptic loosening, infection, and revision for any cause.

RESULTS

The mean Knee Society Score was good for the pain score (42.2, range 10-50) and fair for the function score (60.6, range 0-100). Four deep infections (21.1%) were successfully treated with mobile parts exchange and debridement. Three patients presented femoral osteolysis ≥5 years after the DFR. Survivorship for aseptic loosening was 100% at four years, 81.8% after five years and 53.3% after eight years.

CONCLUSIONS

TKA with DFR is a valuable option for patients with a severe bone loss and poor bone quality in the distal femur. DFR restores an acceptable quality of life but is related to an important complication rate.

Periprosthetic Fractures after Total Knee Arthroplasty: the Influence of Pre-Operative Mechanical Factors versus Intraoperative Factors

Introduction: Periprosthetic fractures are a devastating complication following total knee arthroplasty. Little is known about the effect of mechanical factors on the incidence of periprosthetic fractures. The aim of this study was to examine the correlation between pre-operative mechanical factors, like side of surgery, coronal alignment and pre-operative range of motion and intra-operative factors, and the incidence of a periprosthetic fracture, following primary total knee arthroplasty (TKA).

Materials and Methods: Forty-two patients with periprosthetic fractures (PPF) after primary TKA were identified from our hospital arthroplasty registry. These patients were matched two-to-one for gender and age at primary knee arthroplasty to 84 patients without PPF. The incidence of periprosthetic fracture with regards to laterality, coronal alignment and pre-operative range of motion was analysed. Intra-operative factors like implant type, patellar resurfacing and notching were also analysed using logistic regression.

Results: Coronal alignment, pre-operative range of motion and patella resurfacing were not significant predictors of periprosthetic fractures. Anterior femoral notching was found to be significantly higher in the fracture group with an odds ratio of 17. Left sided surgery was also significantly higher in the periprosthetic fracture group.

Conclusion: Periprosthetic fractures are 17 times more likely to occur in a knee with anterior femoral notching. Preoperative factors like coronal alignment and poor preoperative range of motion do not seem to increase the risk of periprosthetic fractures after TKA.

Does Femoral Notching During Total Knee Arthroplasty Influence Periprosthetic Fracture. A Prospective Study

BACKGROUND

Notching of the anterior femoral cortex during total knee arthroplasty (TKA) has been attributed to cause supracondylar fractures of the femur. Anatomic variations in the femur bone in different races make notching inevitable when standard designs of prostheses are used. The objective of this study is to determine the prevalence of notching when a PFC Sigma knee was used in an Indian population sample using the anterior referencing system and to assess the frequency of femoral shaft fractures in these cases.

METHODS

This is a single-center, prospective study. All patients undergoing TKA were recruited and followed up for a minimum of 2 years. All patients had a PFC Sigma knee (DePuy Synthes), and the anterior referencing system was used for implantation. The Knee Society Score was used for outcome scoring and the Gujarathi's schema for the grading of notching. Radiological outcomes were evaluated by an independent observer. Linear regression analysis assessed the effect of notching on range of motion and final score.

RESULTS

Of the 200 cases, 21% had varying degrees of notching. Grade I was seen in 13%, grade II in 6.5%, grade III in 1%, and grade IV in 0.5% in this series. There was no supracondylar fracture in 2 years. Notching had no bearing on the range of movement or outcome scores.

CONCLUSION

Although notching is best avoided, this study has shown no correlation between notching and supracondylar fracture of the femur following TKA. It does not appear to have any bearing on the range of movement or final outcome scores.

Flexed femoral component improves kinematics and biomechanical effect in posterior stabilized total knee arthroplasty

PURPOSE

The kinematics and biomechanics of the knee joint are important in ensuring patient satisfaction and functional ability after total knee arthroplasty (TKA). There has been no study on knee joint mechanics with regard to the sagittal alignment of the femoral component. The objective of this study is to determine the extent of the impact of the femoral component's sagittal alignment on kinematics and biomechanics.

METHODS

A validated computational TKA model was used. The femoral component was simulated at - 3°, 0°, 5°, and 7° of flexion in the sagittal plane. This study evaluated the tibiofemoral (TF) joint kinematics, contact point, quadriceps force, and contact stress on the patellofemoral (PF) joint under a deep-knee-bend condition.

RESULTS

The kinematics of the TF joint in the posterior direction increased with the flexion of the femoral component position. For all tasks, the overall posterior locations of the TF contact points were observed in the medial and lateral compartments as the femoral component flexion angle increased. The quadriceps force and contact stress on the PF joint decreased with the femoral component flexion.

CONCLUSION

This study found that the femoral component sagittal position is an important factor in knee joint mechanics. In this study, the flexion of femoral component showed a stable reconstruction of the knee extensors' mechanism. Surgeons may consider neutral-to-mild flexed femoral component position, without concerns of anterior notching of the femoral cortex.

Is the fracture pattern in periprosthetic fractures around the knee related with the anterior femoral notch?

INTRODUCTION

Periprosthetic fractures around the knee (PPF) are a devastating complication of total knee arthroplasty (TKA). Anterior femoral notching during TKA is considered a risk factor for PPF. The aim of this paper is to determine if an anterior femoral notch after total knee arthroplasty may affect the fracture pattern when a PPF appears postoperatively.

MATERIAL AND METHODS

50 patients diagnosed in our centre of a PPF from January 2010 to December 2013 were retrospectively enrolled. 100 patients who underwent a total knee arthroplasty without fracture were randomly obtained as a control group. Evidence of the notch was searched in both groups in postoperative X-rays. In the PPF group, distance from the shield of the femoral component to the most distal (d) and proximal (D) point of the fracture were measured.

RESULTS

Two different groups were obtained: 1) d = 0 (33 out of 50 patients); the fracture is supposed to be related with the notch as it's a theoretically weaker area. 2) d > 0 (17 out of 50 patients); the fracture pattern has no relationship with the notch. Prevalence of patients suffering a fracture in the shield of the prosthesis (d = 0), was similar in both patients with notch (66,7%) and without it (68%).

CONCLUSIONS

In conclusion, fracture pattern is not related with the existence of a femoral notch in the clinical setting.

An alternative treatment for osteoporotic Su Type III periprosthetic supracondylar femur fractures: Double locking plate fixation

Introduction

Patients with Su Type III fractures based on total knee arthroplasty (TKA) constitute a patient group with problematic treatment and management. Although it has difficulties, open reduction and internal fixation is one of the treatment options.

Method

A retrospective evaluation was made of 22 patients surgically treated in our clinic with double locking, low contact titanium plate and screw for a Su Type III periprosthetic fracture based on TKA. The patients were evaluated with bone mineral densitometry, postoperative Knee Society Score (KSS), WOMAC and radiological evaluations.

Results

The mean follow-up period of the patients was 68.6 ± 15.5 months, with pain-free weight-bearing determined at 4.9 ± 1.1 months and mean radiological union at 18.5 ± 4.3 weeks. Revision was required because of non-union in 2 (9.09%) cases. The postoperative KSS value was 81.8 ± 7.8, the WOMAC value was 78.1 ± 5.3 and the T-score was −3.3 ± 0.3. At the final follow-up examination, a correction loss (4.9° ± 1.5°) was determined in the mean knee valgus angle according to the mechanical axis, which was statistically significant but remained within the physiological limits (p = 0.21).

Conclusion

In addition to providing the advantages of rigid fixation together with early and effective rehabilitation, satisfactory clinical and radiological results were obtained with the application of double locking plate and screw in the treatment of periprosthetic femoral fractures based on TKA, with osteoporosis.

Level of evidence

Level IV, Therapeutic study.

What Are the Preoperative Outcome Measures That Predispose to Periprosthetic Fractures After Primary Total Knee Arthroplasty?

BACKGROUND

There is little known in the literature about whether preoperative patient-reported outcome measures (PROMs) would affect the risk of periprosthetic fractures (PPFs) after primary total knee arthroplasty (TKA). Our study aims to evaluate the predictive values of PROMs on PPF after primary TKA. We hypothesize that poorer PROMs are associated with a higher risk of PPF after primary TKA.

METHODS

We reviewed prospectively collected data in our hospital arthroplasty registry. Patients who sustained PPF after primary TKA between 2000 and 2015 were identified. Forty-two patients were identified and matched for gender, age, and body mass index to a control group of 84 patients who had primary TKA without PPF in a 2:1 ratio. Preoperative demographics, Short Form-36 (SF-36) scores, Oxford Knee score and Knee Society Score were evaluated. Variables of PROMs were entered into a multivariate logistic regression model. A variable was considered to be a significant predictor if its odds ratio was significant at P < .05.

RESULTS

After multivariate regression analysis, SF-36 subdomains of physical functioning (PF) and vitality (VT) were identified as significant predictors for PPFs after primary TKA. A lower SF-36 PF and VT scores were associated with higher risks of sustaining a PPF after primary TKA.

CONCLUSION

From our study, low preoperative SF-36 PF and VT scores are associated with a higher risk of PPFs after primary TKA. These results can allow the preoperative identification of patients at higher risk of PPF, and appropriate preoperative counseling, optimization, and close follow-up can be instituted for this at-risk group.

[Periprosthetic fractures following total hip and knee arthroplasty: Risk factors, epidemiological aspects, diagnostics and classification systems]

Periprosthetic fractures following hip and knee arthroplasty are potentially severe complications. As a fundament in diagnostic and therapeutic procedures, specific classification systems are necessary to ensure an optimal individualized treatment of these sometimes complicated fractures. This review article summarizes the epidemiological aspects, risk factors and diagnostics of periprosthetic hip and knee fractures. The most frequently used location related fracture classifications systems are explained. In addition, the recently introduced unified classification system (UCS), which is applicable to any location of periprosthetic fractures, is described in detail. Initial studies have shown a reliable applicability of the UCS to periprosthetic hip and knee fractures.

Femoral sizer design can increase anterior notching during total knee arthroplasty

BACKGROUND

The anteroposterior (AP) portions of the distal femur are generally resected externally rotated relative to the posterior condylar line (PCL) in non-navigated/measured-resection total knee arthroplasty (TKA). Some femoral sizing devices allow rotational adjustment before sizing (rotation-modified sizing devices), while others do not (rotation-unmodified sizing devices). When rotation-unmodified sizing devices are used, the stylus attached to the sizing device identifies the proximal/anterior flange cut assuming the femoral component is aligned parallel to the PCL. However, if the AP cutting device is externally rotated then unexpected notching of the anterior cortex can occur.

METHODS

We simulated TKA surgery in 100 Japanese varus osteoarthritic knees using three-dimensional planning software. The femoral component was aligned parallel to the PCL and the AP component position was determined so proximal anterior flange was just touching the anterior cortex. Next, the femoral component was externally rotated parallel to the surgical epicondylar axis (SEA). If the proximal anterior flange penetrated femoral bone, the length and thickness of anterior notching were measured.

RESULTS

The proximal anterior flange rested on the anterior cortex or penetrated the femoral bone in all knees. There was a strong positive correlation between PCA and length of anterior notching. Anterior notching more than 10mm length or one-millimeter thickness occurred in most cases (82.4% and 70.6%, respectively) where the posterior condylar angle (PCA) was more than four degrees.

CONCLUSIONS

Anterior femoral notching is influenced by the design of the femoral sizing guide and subsequent rotation of cutting blocks, especially in knees with a large PCA.

Femur bowing could be a risk factor for implant flexion in conventional total knee arthroplasty and notching in navigated total knee arthroplasty

PURPOSE

This study aimed to investigate the relationship between preoperative femoral axes and femoral implant position and to determine how femoral sagittal axes, including femoral anterior bowing, influence the femoral component position in total knee arthroplasty (TKA).

METHODS

The relationship between femoral axes (femoral anterior bowing, mechanical axis and the anterior cortical line, intramedullary axis) and implant position was compared in 50 conventional and 50 navigated TKAs. Outliers with more than a 3° margin of error in placement of the femoral component compared with the mechanical axis in the sagittal plane were calculated.

RESULTS

The femoral component flexion angle was 3.1° in the conventional group and 1.6° in the navigation group (p < 0.001). Anterior femoral bowing correlated positively with the angle between the mechanical axis and implant (r = 0.360, p = 0.010) in the conventional group and negatively with the angle between the anterior cortical line and flange of the femoral component (r = -0.355, p = 0.010) in navigated TKAs. Incidence of outliers was 48 % (24 patients) in the conventional group compared with 10 % (five patients) in the navigated group (p = 0.008).

CONCLUSIONS

Femoral anterior bowing was an influential factor for implant position and could be a risk factor for both femoral implant flexion in conventional TKAs and notching in navigated TKAs. The results of this study should be considered by surgeons when assessing the risk factors for femoral geometry before performing TKAs, as these results may help them to avoid an overly flexed or extended position of the femoral component, which would affect clinical long-term survival.

LEVEL OF EVIDENCE

Retrospective comparative study, Level III.

Periprosthetic femoral fractures--incidence, classification problems and the proposal of a modified classification scheme

INTRODUCTION

The increasing incidence of periprosthetic fractures correlates directly with the year-after-year increasing frequency of primary joint replacement surgery. The most common fracture localisation is the femur. The undisputed leader in frequency is the fracture that occurs around a total hip arthroplasty. Unfortunately, no general epidemiologic data exist dealing with exact fracture incidence numbers. Furthermore, existing classifications are lacking important information like time point of fracture occurrence, type of the implanted prosthesis and implantation technique (cemented vs. cementless). Additionally, information about mechanical quality of the bone structure and the fracture type are also missing in part.

METHODS

We scanned the literature for adequate and widely used classifications in the field of hip and knee arthroplasty. In a next step we analyzed those classification systems in order to find out to what extent they are able to describe the specific aspects of the fracture event. Therefore we compared the existing classifications and presented their most relevant emphasis. Furthermore, we looked at our own patient population to evaluate incidence of fracture occurrence over time and percentage of loosened components.

RESULTS

The existing classification systems address themselves specifically to the task of describing fracture localization and to some extent fracture type, or combine these two in order to calculate the possibility of loosening of the implanted prosthesis. Some of the important criteria like mechanical quality of the bone stock, primary implantation technique or time point of the prosthesis loosening (prior to or because of the fracture) remain ignored. The incidence of periprosthetic femur fractures at our department increased approximately 2.5 fold over the past two decades. The risk of suffering from a periprosthetic fracture was substantially higher after THA than after TKA. We observed a loose femoral component of the THA in about 45 % of the cases. Finally, we postulate the application of a modified classification for periprosthetic fractures as an alternative to the already published ones; not only for the femur, but also universally for all joints with an arthroplasty.

CONCLUSION

The classification that is introduced in this study allows, in our opinion, a differentiated reflection of the given post-traumatic pathologic changes and enables the description of the fracture itself according to a generally accepted fracture classification scheme.

Periprosthetic fractures: concepts of biomechanical in vitro investigations

PURPOSE

Experimental in vitro studies investigating periprosthetic fractures after joint replacement are used increasingly. The purpose of this review was to deliver a condensed survey of studies in order to provide researchers with an overview of relevant scientific results and their clinical relevance.

METHODS

A literature search was conducted to obtain all available papers dealing with periprosthetic fractures, with particular attention being paid to articles with an experimental research design. Study goals, scientific methods and results, their interpretation and clinical relevance were assessed and compared. The main focus was on comparability with clinical fracture patterns and physiological joint loads.

RESULTS

Excluding duplicates, 24 studies with regard to artificial hip, knee and shoulder joints were found dating back to August 2000. Almost all studies were performed quasi-statically and without consideration of muscle forces and thus reflect selected loading conditions and no dynamic situation during activities of daily living (ADL). Various experimental protocols were used, differing in the choice of experimental material, implant and fixation system and load application.

CONCLUSIONS

In vitro studies regarding periprosthetic fracture research allow controlling for disturbances, such as clinically occurring risk factors like reduced bone mineral density (BMD) or greater patient age. Notwithstanding, due to methodological differences, comparisons between studies were possible to a limited degree only. For this reason, and because of quasi-static loading typically applied, results can only be partially applied to clinical practice.

Risk of Anterior Femoral Notching in Navigated Total Knee Arthroplasty

Background

We retrospectively investigated the prevalence of femoral anterior notching and risk factors after total knee arthroplasty (TKA) using an image-free navigation system.

Methods

We retrospectively reviewed 148 consecutive TKAs in 130 patients beginning in July 2005. Seventy knees (62 patients) underwent conventional TKA, and 78 knees (68 patients) received navigated TKA. We investigated the prevalence of femoral anterior notching and measured notching depth by conventional and navigated TKA. Additionally, the navigated TKA group was categorized into two subgroups according to whether anterior femoral notching had occurred. The degree of preoperative varus deformity, femoral bowing, and mediolateral suitability of the size of the femoral component were determined by reviewing preoperative and postoperative radiographs. The resection angle on the sagittal plane and the angle of external rotation that was set by the navigation system were checked when resecting the distal femur. Clinical outcomes were compared using range of motion (ROM) and the Hospital for Special Surgery (HSS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAX) scores between the two groups.

Results

The prevalence of anterior femoral notching by conventional TKA was 5.7%, and that for navigated TKA was 16.7% (p = 0.037). Mean notching depth by conventional TKA was 2.92 ± 1.18 mm (range, 1.8 to 4.5 mm) and 3.32 ± 1.54 mm (range, 1.55 to 6.93 mm) by navigated TKA. Preoperative anterior femoral bowing was observed in 61.5% (p = 0.047) and both anterior and lateral femoral bowing in five cases in notching group during navigated TKA (p = 0.021). Oversized femoral components were inserted in 53.8% of cases (p = 0.035). No differences in clinical outcomes for ROM or the HSS and WOMAX scores were observed between the groups. A periprosthetic fracture, which was considered a notching-related side effect, occurred in one case each in the conventional and navigated TKA groups.

Conclusions

Surgeons should be aware of the risks associated with anterior femoral notching when using a navigation system for TKA. A modification of the femoral cut should be considered when remarkable femoral bowing is observed.

A Unique Pattern of Peri-Prosthetic Fracture Following Total Knee Arthroplasty: The Insufficiency Fracture

An isolated periprosthetic compression fracture following total knee arthroplasty has not been described in periprosthetic fracture classifications. Thus, the purpose is to describe this unique type of fracture based on clinical and radiographic analysis and identify the incidence and potential risk factors of this fracture. A retrospective chart review was performed from a database of 5864 primary total knee. A total of 56 (0.9%) periprosthetic fractures were identified with 15 (26.8%) of them demonstrating an isolated lateral compression fracture. Patients exhibiting this fracture pattern had a mean preoperative varus deformity of 176.3° and had poor bone quality (T score: -2.1). It is important to recognize that a compression fracture is not an infrequent finding and that further workup maybe warranted when clinical suspicion is high.

A new method for calculating femoral anterior cortex point location and its effect on component sizing and placement

BACKGROUND

Variation in anterior femoral cortex morphology can cause improper component placement and alignment. When surgical inaccuracies occur, the mechanical properties of the distal femur may be altered, which could result in lower surgical success rates and an increased chance of postoperative complications.

QUESTIONS/PURPOSES

The purpose of the study is to come up with a reproducible computational algorithm to simulate what the surgeon does in the operating room. This method could help in surgical preplanning, patient-specific instruments, and implant design. From there, we evaluated (1) the angular difference between reference alignment axes; and (2) whether the location of the anterior cortex point and alignment axes had an effect on implant placement and amount of bone resected in seven implant systems.

METHODS

We analyzed 470 femurs from white and black individuals. Two points were defined using automatic three-dimensional landmarking: sizing point and femoral resection anterior cortex (FRAC) point. Alignment axes including the transepicondylar, posterior condylar, distal anatomical (DAA), and mechanical axes (MAs) were automatically calculated and used along with the resection point to define the anterior reference plane. Two mechanical axes were defined for the purpose of this study: MA-1 is a virtual construct used in navigated surgeries defined as the axis joining the center of the femoral head and the knee center and MA-2 was calculated as the axis joining the center of the femoral head and distal exit point of the DAA. Amounts of anterior, posterior, and distal resected bone were calculated along with the difference in orientation between the alignment axes.

RESULTS

The mean angular difference between transepicondylar axis and posterior condylar axis (PCA) was 5.44°±2.99°. All seven implant families showed more total bone resection on both the lateral and medial sides when the implants were aligned using MA-2 and PCA+3 of external rotation (PCA+3) when compared with using MA-1 and PCA+3 (p<0.01). Using MA-2 and PCA+3 as an alignment method reduced the amount of bone resection on both medial and lateral anterior surfaces from 1 to 2 mm.

CONCLUSION

The FRAC point is a key landmark in the placement and sizing of the femoral component. Improper sizing, notching, undercutting, or overstuffing can occur based on selecting the highest or lowest cortex point.

CLINICAL RELEVANCE

Balanced placement, prevention of notching, and anterior and posterior cut balancing were accomplished when using the suggested cortex point.

Periprosthetic fractures around total knee arthroplasty

Periprosthetic fractures around total knee replacements were first reported more than 30 years ago. They are becoming more common. Various associated risk factors have been described. Treatment options for femoral fractures around total knee replacements include non-operative management, locked plates, retrograde intramedullary nails and revision arthroplasty. Periprosthetic fractures of the tibia and patella are also described, but are less common. This review article provides an overview of the epidemiology and frequency of periprosthetic fractures around total knee replacement, their initial assessment and the current treatment options available.

Distal femoral replacement for selective periprosthetic fractures above a total knee arthroplasty

BACKGROUND AND AIM

The management of distal femur periprosthetic fractures in the elderly remains a challenge. The aim of this study was to evaluate the results of distal segmental femur replacement as an alternative to fixation in complex distal femoral periprosthetic fractures in elderly patients.

METHODS

Twelve patients were included in this prospective study, with a mean age of 78 years (range 68-90 years); incidentally, all were female. Fractures of the distal femur were classified as per Kim et al.'s classification (Clin Orthop Relat Res 446:167-175, 2006); our series included eight patients with type III and four patients with type II periprosthetic fractures. All 12 patients were treated with segmental distal femur replacement (Zimmer Inc., Warsaw, IN, USA). Nine patients required 90 cm and three patients required 130 cm of distal femur segment with a rotating hinge knee prosthesis.

RESULTS

The mean follow up period was 20 months (range 15-28 months), with no major surgical complications reported. The mean duration of hospital stay following surgery was 12 days (range 7-36 days). All patients were mobilising full weight-bearing by day 3. All patients returned to their prior living arrangements. Ten patients returned to their original domicile, with one patient being discharged to a care home requiring minimal ambulatory assistance. The remaining two patients returned to their care homes.

CONCLUSIONS

WOMAC scores improved from the pre-injury state with a mean of 49.62 to 72.54 post-surgery (p-value of 0.0001). The Knee Society scores, possible only following surgery, had a mean value of 72. The mean VAS pain score was 1.75 (0 = no pain to 10 = worst pain ever felt). The average range of knee flexion was from 4° to 89° (range -5° to 110°). The mean SF-36 physical functioning score was 45.64 [range 40.70-48.90; standard deviation (SD) -2.62] and the mean SF-36 mental functioning score was 52.94 (range 45.8-57.70; SD -3.38).

Outcome and incidence of periprosthetic supracondylar femoral fractures in TKA

BACKGROUND

Periprosthetic supracondylar femoral fractures following total knee arthroplasty (TKA) are infrequent, but is a devastating complication. The purpose of this study was to evaluate the incidence and outcomes of periprosthetic supracondylar femoral fractures following TKA using nonoperative as well as open reduction and internal fixation (ORIF) techniques.

MATERIALS AND METHODS

Between January 2004 and December 2010, we followed 3,920 operated patients of total knee arthroplasty (TKA) and identified 23 patients with periprosthetic supracondylar fractures. A retrospective analysis of the records of these patients was conducted. Details regarding pre fracture status, treatment offered and the present status were also recorded and analyzed. Time from index arthroplasty to periprosthetic fracture ranged from five days to six years. There were 17 women and 6 men and the average age was 68.26 years (range 52-83 years). Of the 23 patients, 20 patients were treated by operative method, whereas only three patients with relatively undisplaced fractures were treated nonoperatively.

RESULTS

The total incidence of periprosthetic fractures in operated cases of TKA was 0.58%. Three patients had infection after surgery. As per radiological assessment, two of three conservatively treated cases had malunion, whereas among 20 cases treated operatively, 16 had primary union with one malunion. Two patients had union after bone grafting, whereas two had nonunion. The average reduction in the knee score after fracture was 20.53%. Twenty one patients were able to achieve limited but independent activity.

CONCLUSIONS

Desirable results for periprosthetic fractures can be obtained if proper and timely intervention is done, taking into account the other comorbid conditions. However, short duration of followup and small number of patients were major limiting factors in this study.

Functional outcome of total knee arthroplasty after periprosthetic distal femoral fracture

A prospective matched cohort study was performed to compare functional outcomes between 28 patients with periprosthetic femoral fractures and 28 with primary total knee arthroplasties (TKA). The mean follow-up was 6.7 years (range, 5-9). Radiographic osteopenia was a predisposing factor, but not notching, body mass index, or preinjury knee scores or motion. At last follow-up, the Knee Society scores, knee motion, Womac, and SF-12 were significantly lower in the fracture group, and were significantly decreased compared to the preinjury status. We found that periprosthetic distal femoral fracture after TKA worsens functional outcomes at the medium term, but arthroplasty complication and survival rates were similar in both groups.

Influence of the sagittal reference axis on the femoral component size

The sagittal reference axes used for setting of the femoral component vary according to surgical methods. The purpose of the study was to clarify the relation of the sagittal reference axis with the anteroposterior (AP) length of the distal femur at the time of determining the femoral component size. Fifty consecutive varus osteoarthritic knees with primary total knee arthroplasty were divided into two groups according to surgical methods (intramedullary and extramedullary groups) and were examined based on CT data. AP length of the distal femur changed nearly 0.6mm corresponding to each 1° flexion of the sagittal reference axis. The size of the femoral component in the intramedullary group was larger than that in the extramedullary group. The sagittal reference axis had an influence on the component size.

Periprosthetic fractures around total knee arthroplasty

INTRODUCTION

The number of total knee arthroplasties performed continues to rise annually and it would be expected that complications, which include periprosthetic fractures, will also therefore become more commonplace. This article reviews the current literature regarding this injury and identifies the treatment principles that enable patients to regain optimal function.

METHODS

A comprehensive search of the Pubmed and Embase™ databases was performed to identify relevant articles. Keywords and MeSH (Medical Subject Headings) terms included in the search strategy were 'periprosthetic fracture(s)', 'femur', 'tibia', 'patella(r)', 'complication(s)', 'failure(s)', 'risk(s)', 'prevalence', 'incidence', 'epidemiology' and 'classification(s)'. The search was limited to all articles published in English and reference lists from the original articles were reviewed to identify pertinent articles to include in this review. A total number of 43 studies were identified.

RESULTS

Common treatment aims have been identified when managing patients with a periprosthetic fracture around total knee arthoplasty. The main criterion that determines which option to choose is the degree of remaining bone stock and the amount of fracture displacement.

CONCLUSIONS

Treatment of a periprosthetic fracture around total knee arthroplasty will either be non-operative, osteosynthesis or revision arthroplasty. It is imperative that a suitable option is chosen and based on the published literature, pathways are outlined to aid the surgeon.

Improved stability with intramedullary stem after anterior femoral notching in total knee arthroplasty

PURPOSE

It has been hypothesized that femoral notching in total knee arthroplasties weakens the cortex of the femur, which can predispose to femoral fractures in the postoperative period. Some authors suggest that patients who sustain inadvertent notching should have additional protection in the postoperative period, and consideration should be given to the use of prophylactic femoral stems. In this case, a question can be raised: Is the use of femoral stem in an anterior femoral notching an effective way to reduce the fracture risk? We hypothesized that for a larger notch, the use of a femoral stem does not decrease considerably the stress-riser at the notch edge, and the use of stem is not enough to reduce the risk of fracture.

METHODS

In the present in vitro study, twelve synthetic femurs were selected and used for the experiments under two load scenarios. Femoral components with and without femoral stems were implanted in femurs with different notch sizes to predict experimentally the strain levels at the notch edge with the use of fiber Bragg gratings and at notch region with strain gauges.

RESULTS

Despite the global strain reduction in stemmed condition, at the notch edge, the strain behavior was dissimilar for the different notch depths. For notch depths lower than 5 mm, the use of stem reduces the strain level at the notch edge to values below the intact femur condition, while for depths greater or equal to 5 mm, the strain levels at the notch edge were higher than the intact femur condition with values ranging from +10 to +189%.

CONCLUSIONS

The present study suggests the use of a prophylactic stem for notch depths greater than 5 mm. For notch depths below 5 mm, the fracture risk due to strain increase at the notch edge seems to be low in the stemless condition.

An unusual way of intramedullar fixation after a periprosthetic supracondylar femur fracture

Periprosthetic supracondylar femoral fractures after a total knee arthroplasty are difficult surgical problems. We report a case of an 84-year-old woman with an osteoporotic fracture that was not deemed amenable to conventional treatment. In this case, a complete consolidation was achieved by using a proximal femur nail antirotation nail upside down and through the fracture for fixation.

Association of peptic ulcer disease and pulmonary disease with risk of periprosthetic fracture after primary total knee arthroplasty

OBJECTIVE

To assess the association of specific comorbidities with periprosthetic fractures after primary total knee replacement (TKR).

METHODS

We used the prospectively collected data in the Mayo Clinic total joint registry from 1989-2008 on all patients who had undergone primary TKR. The outcome of interest was postoperative periprosthetic fractures during followup. The main predictors of interest were comorbidities grouped from the validated Deyo-Charlson index. Multivariable-adjusted Cox regression analyses were adjusted for sex, age, body mass index (BMI), American Society of Anesthesiology (ASA) class, operative diagnosis, and implant fixation. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated.

RESULTS

We included 17,633 primary TKRs with a mean followup of 6.3 years. The mean age was 68 years, 55% were women, and the mean BMI was 31 kg/m(2) . There were 188 postoperative periprosthetic fractures on postoperative day 1 or later; 162 fractures (86%) occurred on postoperative day 90 or later. In multivariable analyses that simultaneously adjusted for all comorbidities and other variables (age, sex, BMI, ASA, operative diagnosis, and cement status), the following 2 conditions were significantly associated with an increased hazard of postoperative periprosthetic fractures: peptic ulcer disease (HR 1.87, 95% CI 1.28-2.75; P = 0.0014) and chronic obstructive pulmonary disease (HR 1.62, 95% CI 1.10-2.40; P = 0.02).

CONCLUSION

Peptic ulcer disease and chronic obstructive pulmonary disease are associated with a higher risk of periprosthetic fractures after primary TKR. This may be related to the disease or its treatments, which need further study. Identification of specific risk factors may allow for implementation of intervention strategies to reduce this risk.

Surgical treatment options in patients with impaired bone quality

BACKGROUND

Bone quality should play an important role in decision-making for orthopaedic treatment options, implant selection, and affect ultimate surgical outcomes. The development of decision-making tools, currently typified by clinical guidelines, is highly dependent on the precise definition of the term(s) and the appropriate design of basic and clinical studies. This review was performed to determine the extent to which the issue of bone quality has been subjected to this type of process.

QUESTIONS/PURPOSES

We address the following issues: (1) current methods of clinically assessing bone quality; (2) emerging technologies; (3) how bone quality connects with surgical decision-making and the ultimate surgical outcome; and (4) gaps in knowledge that need to be closed to better characterize bone quality for more relevance to clinical decision-making.

METHODS

PubMed was used to identify selected papers relevant to our discussion. Additional sources were found using the references cited by identified papers.

RESULTS

Bone mineral density remains the most commonly validated clinical reference; however, it has had limited specificity for surgical decision-making. Other structural and geometric measures have not yet received enough study to provide definitive clinical applicability. A major gap remains between the basic research agenda for understanding bone quality and the transfer of these concepts to evidence-based practice.

CONCLUSIONS

Basic bone quality needs better definition through the systematic study of emerging technologies that offer a more precise clinical characterization of bone. Collaboration between basic scientists and clinicians needs to improve to facilitate the development of key questions for sound clinical studies.

Biomechanical evaluation for mechanisms of periprosthetic femoral fractures

BACKGROUND

There are a number of biomechanical tests for various treatment options of periprosthetic femoral fractures, but different loading modalities prelude their direct comparison. This study was designed to develop an experimental model of osteoporotic bone fractures near the femoral stem that is based on a simple testing protocol to increase the reproducibility. In addition, we wanted to clarify whether a femoral prosthetic stem reduces the femoral fracture strength.

METHODS

Twenty human cadaveric femurs were harvested, and five groups were randomized on the basis of the bone mineral density using a pQCT device. The specimens of three groups were provided with a cemented Exeter V40 stem and loaded to failure with torsion (I), anterior (II), and lateral load (III). The femurs of groups IV and V remained uninstrumented and were tested in a four-point bending assay similar to groups II and III. All biomechanical testings were realized with a servohydraulic testing machine (MTS).

RESULTS

There was no significant difference regarding bone mineral density of all groups. Torsional testing generated proximal intertrochanteric fractures and anterior loading resulted exclusively in supracondylar fractures. Introducing the force from the lateral side, all fracture lines occurred close to the tip of the stem, similar to a Vancouver-B fracture. Assuming that lateral load application is a main responsible mechanism of periprosthetic femoral fracture near the tip of the stem, the fracture strength of instrumented femurs was significantly reduced (group III: 4,692 N vs. group V: 6,931 N; p < 0.05).

CONCLUSION

Prosthetic stems reduce femoral fracture strength significantly. In an osteoporotic bone model, a four-point bending test with lateral load application seems to be a suitable approach.

Periprosthetic fractures of the femur after total knee arthroplasty

Periprosthetic fracture following total knee arthroplasty is a potentially serious complication. This injury can involve the distal femur, proximal tibia or the patella. This review article analyzes the prevalence, risk factors, classification and treatment options for periprosthetic fractures of the femur.

Differences between sagittal femoral mechanical and distal reference axes should be considered in navigated TKA

In computer-assisted TKA, surgeons determine positioning of the femoral component in the sagittal plane based on the sagittal mechanical axis identified by the navigation system. We hypothesized mechanical and distal femoral axes may differ on lateral views and these variations are influenced by anteroposterior bowing and length of the femur. We measured angles between the mechanical axis and distal femoral axis on 200 true lateral radiographs of the whole femur from 100 adults. We used multivariate linear regression to identify predictors of differences between the axes. Depending on the method used to define the two axes, the mean angular difference between the axes was as much as 3.8 degrees and as little as 0.0 degrees, with standard differences ranging from 1.7 degrees to 1.9 degrees. Variation between the two axes increased with increased femoral bowing and increased femoral length. Surgeons should consider differences between the mechanical axes and distal femoral axes when they set the sagittal plane position of a femoral component in navigated cases. Our findings also may be relevant when measuring rotation of the femoral component in the sagittal plane from postoperative radiographs or when interpreting femoral component sagittal rotation results reported in other studies.

Locked plating of supracondylar periprosthetic femur fractures

Fifty periprosthetic supracondylar femur fractures above a total knee arthroplasty were reviewed. Fractures were closed Lewis and Rorabeck type II with a stable prosthesis. Twenty-nine patients (group I), were treated with locked condylar plating. Twenty-one patients (group II) were treated with nonlocked plating systems or intramedullary fixation. Minimum follow-up was 1.7 years. There were 5 malunions (20%) in group I and 9 (47%) in group II (P < .05). There were no nonunions in group I and 3 (16%) in group II. Complication rates were 12% in group I, compared to 42% in group II. Group I patients had less operative blood loss, healed in better alignment, and had greater knee motion. All 7 patients treated with a retrograde intramedullary nail developed a malunion or nonunion. Locked plating is a reliable treatment for periprosthetic supracondylar femur fractures. We experienced a lower complication, revision, malunion, and nonunion rate with locked plating versus conventional treatment options.

Low complication rate of LISS for femur fractures adjacent to stable hip or knee arthroplasty

Fractures of the femur after a knee or hip arthroplasty historically have been plagued with high complication rates. The Less Invasive Stabilization System (LISS) has theoretical advantages of improved biomechanics and limited insult to the bone's vascular supply. We theorized that the LISS would have a lower complication rate than historical controls for these fractures. Patients who were treated with a LISS at two Level I trauma centers from July 2001 to July 2003 were prospectively followed up. The inclusion criteria were an acute fracture of the femur treated with a LISS in a patient with a stable ipsilateral total knee prosthesis and/or hip pros- thesis. There were 24 patients in the study group. The injury mechanism was a low-energy fall for all patients. All patients were females with an average age of 79.5 years (range. 64-93 years). Ten patients had ipsilateral hip arthroplasties, nine patients had ipsilateral total knee arthroplasties, and five patients had knee and hip arthroplasties. Followup was at an average of 48 weeks (range, 17-101 weeks). Eighteen of the 19 fractures in the surviving patients with followup healed uneventfully for a complication rate of 5.2%. One fracture was complicated by hardware pullout and was revised to a longer LISS that healed uneventfully. We think our data show that our patients had a low complication rate compared with that of historical controls, and we suggest that the LISS may be an appropriate treatment alternative for femur fractures associated with stable hip or knee prostheses.

LEVEL OF EVIDENCE

Therapeutic, Level IV.

Notching of the anterior femoral cortex during total knee arthroplasty characteristics that increase local stresses

Notching of the anterior femoral cortex during primary total knee arthroplasty can occur when making an anterior femoral bone cut. To examine the increased stress caused by a notch, we used a validated 3-dimensional finite element model of the femur under gait loads. Three factors that affected the stress concentration were identified: First, larger notches associated with increased stress concentrations. Second, sharper notches led to increased local stresses. Third, the proximity of the notch to the prostheses affected the stress concentration. In summary, anterior femoral notches greater than 3 mm with sharp corners located directly at the proximal end of the prosthesis produced the highest stress concentrations and may lead to a significant risk of periprosthetic fracture.

Midterm results of treatment with a retrograde nail for supracondylar periprosthetic fractures of the femur following total knee arthroplasty

OBJECTIVES

Although the short-term results of supracondylar periprosthetic fractures treated with retrograde nailing have been satisfactory, there is always a concern about the long-term survival of the prosthesis. The aim of the study was to evaluate fracture healing and knee functional outcome with a follow-up time of at least 2 years in periprosthetic fractures of the knee treated with a supracondylar nail.

DESIGN

Cohort study.

PATIENTS

There were 9 patients with 10 periprosthetic fractures. In 1 patient, the fracture occurred intraoperatively. In the others, the time between the total knee arthroplasty and the periprosthetic fracture ranged between 2 weeks and 7 years (average time: 2.78 years). The mean follow-up was 34.5 months (25-52 months).

MAIN OUTCOME MEASUREMENTS

The Western Ontario and McMaster Universities index was used to evaluate the functional result postoperatively using the paired t test as the statistical test. Fracture union was assessed with plain x-rays.

RESULTS

All the fractures united within 3 months. One fracture united in extreme valgus (35 degrees) and was revised to a stemmed total knee replacement. There were no infections and no prosthesis loosening. The paired t test before the fracture and after the operation demonstrated no statistically significant differences; however, there was a trend toward lower functional score postoperatively.

CONCLUSIONS

It appears that retrograde nailing is a reliable technique to treat periprosthetic supracondylar fractures. It provides adequate stability until fracture union. The morbidity of the operation is minimal, and the complication rate is low. The midterm results in our study showed that none of the prostheses required revision. In our opinion, it is the treatment of choice for a periprosthetic fracture when the prosthesis is stable.