Lateral Femoral Cortex Research Articles

Radiographic Bone Regeneration and Clinical Outcome With the Wagner SL Revision Stem: A 5-Year to 12-Year Follow-Up Study

We used 79 Wagner SL stems (Sulzer Orthopedics, Baar, Switzerland) in femoral revisions with a minimum 5-year follow-up. There were 11 dislocations. A limb length discrepancy and limp were frequent. One loosened stem was rerevised. The cumulative probability of not having a stem revision for any reason was 92.3% in the best case scenario. Stem subsidence was associated with poor femoral canal filling. Definite proximal new bone regeneration (50 hips) was associated with an absence of major bone defects ( P = .01). Lateral and medial femoral cortex and the outside femoral diameter had increased at the end of follow-up ( P < .001). Wagner SL femoral revision stems can solve difficult cases with major proximal bone defects or periprosthetic fractures. Radiographic bone fixation and bone regeneration were frequent. Dislocations and stem subsidence were also frequent.

Bilateral periprosthetic stress fractures in a juvenile chronic arthritis patient secondary to bilateral genu valgum

Lateral insufficiency fractures following total hip replacement have been reported with the femoral stems positioned in varus, together with osteopenia of the lateral femoral cortex. Any abnormal alignment of the lower limbs, such as genu valgum, will alter the load distribution across the femoral cortices, and repetitive loading during walking will predispose the bones to stress fractures at any stress riser point, such as the tip of a femoral component. Bilateral femoral stress fractures post total hip replacements have not been previously described. We present a 55-year-old woman, diagnosed with juvenile idiopathic arthritis, who had undergone bilateral total hip replacements and bilateral knee replacements. The knees 15 years postoperatively were in valgus and the left knee was extremely stiff, flexing to just 5. The patient presented with bilateral thigh pain, with plain radiographs confirming bilateral periprosthetic fractures of the femur at the tip of well-fixed femoral components. There was no history of injury and her hips were functioning well up to this time. The patient required revision of both hips to long-stem uncemented components, bypassing the fractures, and revision of both knees to stemmed semi-constrained implants, thereby correcting the alignment of both lower limbs. Both fractures healed and the patient is currently pain-free and mobile with walking aids. Surgeons must remain aware that when implants are in situ, abnormal alignments will lead to abnormal forces, and stress fractures are likely to occur at any stress riser around the implant. Avoiding malalignment will avoid this complication.

Morphological analysis of the proximal femur using quantitative computed tomography

The anatomy of the proximal femur was studied in 35 specimens using quantitative computed tomography (QCT) and compared with anatomical sections studied by plane radiography and gross dissection. We found the primary supporting structure of the femoral head to be the primary compressive strut, which is a dense column of trabecular bone projecting from the pressure buttress of the medial femoral neck to the epiphyseal scar. Trabecular bone mushroomed from the epiphyseal scar and terminated at right angles to the cortex of the femoral head. We believe the primary compressive strut is the predominant load-bearing structure connecting the femoral head to the femoral neck, as many specimens lacked continuity of the head cortex to the femoral neck. Based on the CT number, the primary compressive strut had similar bone density to cortical structures such as the lesser trochanter, calcar femorale and posterior lateral femoral cortex. Ward's triangle lacked structural integrity in many cases, and we doubt the significance of tensile trabculae for sharing load. Surgical techniques such as femoral fracture fixation, resurfacing hip arthroplasty and allograft transplantation may benefit from this knowledge.

THE CLASSIC: Complete Replacement Arthroplasty of the Hip by the Ring Prosthesis

THE CLASSIC: Complete Replacement Arthroplasty of the Hip by the Ring Prosthesis

Unstable Pertrochanteric Femoral Fractures

Fractures in the trochanteric region of the femur are classified as AO/OTA 31-A, as they are extracapsular. This report analyzes the relatively rare 31-A3 fracture, which has also been referred to as an "intertrochanteric femur fracture with subtrochanteric extension," "reverse obliquity intertrochanteric femur fracture," "unstable intertrochanteric femur fracture," or a "subtrochanteric femur fracture." The A3 fracture is characterized by having a fracture line exiting the lateral femoral cortex distal to the vastus ridge. Possible fixation constructs include compression hip screws, intramedullary hip screws, trochanteric intramedullary nails, cephalomedullary antegrade intramedullary nails, and 95 degrees plates. Most reports investigating 31-A fractures do not describe the 31-A3 fracture. For this analysis, only reports clearly indicating that the fracture treated was a 31-A3 were included. It should be understood that this approach therefore excludes reports on generic "subtrochanteric fractures" or "intertrochanteric fractures," some of which may have been 31-A3 fractures. To determine the effect of fixation technique for the AO/OTA 31-A3 fracture on rates of union, infection, risk of reoperation, and functional outcomes.

Preliminary stabilization of the less invasive stabilization system.

We describe the use of a universal T-handle chuck to provide preliminary stabilization of the Less Invasive Stabilization System supracondylar femur implant and aiming device. This technique is helpful to maintain the position of the plate against the bone during intraoperative radiographs and initial screw insertion. Use of this simple technique may help avoid the problems that occur when the plate is positioned too far away from the lateral femoral cortex.

Trochanteric slide osteotomy in revision total hip arthroplasty for loosening.

We used a trochanteric slide osteotomy (TSO) in 94 consecutive revision total hip arthroplasties (90 with replacement of both the cup and stem). This technique proved to be adequate for removing the components, with few complications (two minor fractures), and for implanting acetabular allografts (18%) and reinforcement devices (23%). Trochanteric union was obtained in most patients (96%), even in those with septic loosening (18/19), major femoral osteolysis (32/32), or previous trochanteric osteotomy (17/18). TSO is versatile, since it can be extended by a femoral flap (four cases) or a distal femoral window (eight cases). Despite significant bone loss, in 24% of the femora and 57% of the acetabula, favourable midterm results were achieved and only six reoperations were required, Including two for trochanteric nonunion and two for loosening. It leaves the lateral femoral cortex intact so that a stem longer than 200 mm was needed in only 25% of patients. This is a considerable advantage compared with the extended trochanteric osteotomy in which the long lateral flap (12 to 14 cm) requires an average length of stem of 220 mm beyond the calcar. TSO provides an approach similar in size to the standard trochanteric osteotomy but with a rate of nonunion of 4% versus 15%. It reduces the risk of difficulties with removal of the stem, and removes the need for routine distal anchoring of long revision stems. The limited distal femoral compromise is very important in patients with a long life expectancy.

Slipped Capital Femoral Epiphysis – Initial Results of Treatment with Fixclips, a Modification of Kirschner Wire Fixation

26 cases (21 patients) with Slipped Upper Femoral Epiphysis were treated by internal fixation with Fixclips. Of the 19 males and two females with a mean age of 12 l/2 years (range 10–15), 22 were fixed in situ and 4 required Dunn's osteotomies. The Fixclip allows two 2mm K wires, transfixing the proximal femoral epiphysis, to be anchored to the lateral femoral cortex. Post-operatively partial weight bearing was commenced at 6 weeks. The mean follow-up was 17 months (range 8–26), 10 cases being followed up to epiphyseal union. There were no failures of fixation and no significant complications.Given that the size of implant used to treat slipped femoral epiphyses may be related to the chance of developing avascular necrosis, the small cross sectional area of simple K wires offers a potential advantage. The Fixclip prevents K wire penetration or extrusion, previously a problem with this type of fixation. In addition, ease of removal offers a significant advantage given the inevitability that a proportion of these patients will outgrow their primary fixation and require revision of fixation.

Long-term residual musculoskeletal deficits after femoral shaft fractures treated with intramedullary nailing.

Locked intramedullary (IM) nailing has been recognized as one of the most reliable methods for treatment of femoral shaft fractures. Although IM nails are routinely used in the treatment of these fractures, the long-term effects of retained IM nails are unknown. Seventeen patients with radiographically documented healed fracture of femoral diaphysis after locked IM nailing technique were evaluated at a follow-up of at least 18 months postoperatively. All patients had returned to their preinjury level of function and activity before the study. The bone mineral densities (BMD) of the injured and contralateral femora were measured using dual energy x-ray absorptiometry (DEXA). BMD of symmetrical regions in the femoral neck and medial and lateral femoral cortex of the implanted and contralateral femora were compared. Postinjury muscle function was assessed from measurement of the isometric strength of six separate muscle groups (quadriceps, hamstrings, hip extensors, hip flexors, hip abductors, and hip adductors) in treated and control extremities. The average BMD of the femoral neck region of instrumented femora was 9% less than in contralateral control. Within the medial cortex, BMD of the control femora was an average of 20% greater than in the implanted side. In the lateral cortex, the difference averaged 13%. The isometric dynamometric data demonstrated a statistically significant reduction in the strength of the quadriceps of the instrumented extremities as compared with the contralateral ones. There was no significant difference in the strength of the hamstrings, hip extensors, hip flexors, abductors, or adductors. In the control extremities, the average torque generated by isometric contraction of the quadriceps was 3.45+/-1.35 times greater than by the hamstrings. Torque in extension/flexion and abduction/adduction was also observed. Our data suggest that limbs with long-term retained IM nails experience a significant reduction in the femur BMD and quadriceps muscle strength. These findings may not be simply related to the implant, and further study is warranted to determine the causes of these changes.

A SURGICAL GUIDE TO ACCURATELY PLACE PINS OR NAILS WITHIN THE FEMORAL HEAD

The purpose of this study was to demonstrate the accuracy of a novel, surgically useful guide that could place a drill or pin within the femoral head. The radiolucent guide for attachment to the lateral femoral cortex was tested for reproducibility on cadaveric specimens simulating a surgical procedure. The guide allows selection of the three-degree freedom angle of insertion of a drill or pin via two circular channels allowing anterior–posterior or superior–inferior adjustment. The guide can accurately place a pin tip within 2.5–3.8 mm of a desired location. We conclude this guide could be used to accurately place a fibular graft in an osteonecrotic lesion, or place pins or nails during many different surgical procedures such as fractures or slipped capital femoral epiphysis.

Letters to the Editor

Reply to Maquet Dear Sir: We would like to thank Dr. Maquet for his comments. Although the figure is correct in depicting bending loading of the femoral neck, it is misleading and oversimplistic as Dr. Maquet points out because it does not include compressive loads. In a two-dimensional static analysis where the sum of all abductor muscles are reduced to a single, planar vector, the ratio of compressive to bending forces in the femoral neck is approximately three. This compressive force effectively overcomes the superior tensile bending forces that are reduced additionally by an active muscle force as depicted in the figure. More sophisticated analyses account for each abductor muscle, and their three-dimensional force vector as determined by anatomy (cross sectional area), electromyographic data, areas of origin and insertion, and femoral neck angle and version. Regarding the breakage of the upper pin in Figure 6, Dr. Maquet is correct that in an intact proximal femur, the pins are subjected to either compression or tension, depending on their location in the femoral neck. However, after femoral neck fracture, before osseous union, all pins are subjected to cantilever bending and shear. An additional factor that affects whether an implant will break during osseous loading is the quality of fixation, that is, how well the implant is fixed in the femoral head and lateral femoral cortex. Finally, the reference for our statement that the gluteus medius muscle is the main hip abductor was: Clark JM, Haynor DR: Anatomy of the abductor muscles of the hip as studied by computed tomography. J Bone Joint Surg 69A:1021-1031, 1987 . Kenneth A. Egol, MD Kenneth J. Koval, MD Frederick Kummer, PhD Victor H. Frankel, MD New York, NY

CT-based analysis of the geometry of the distal femur

When applying minimally invasive techniques (MIO, Minimally Invasive Osteosynthesis) to the fixation of the distal femur, the surgeon has access to a limited number of anatomical landmarks: namely the articular surface of the distal femur and a small portion of the distal lateral femoral cortex. A detailed knowledge of the local anatomy facilitates the techniques and prevents complications. Using Kirschner wires placed set positions in the distal femur, we analyzed the measurements obtained from the 3D reconstructed helical CT scans of 33 embalmed femora and we report on the anatomy of the distal femur as it relates to supracondylar fracture fixation.

Proximal femur fractures after free vascularized fibular grafting to the hip.

The management of symptomatic femoral head osteonecrosis in young, active patients is troublesome and controversial. At the authors' institution, 707 consecutive free vascularized fibular grafts were performed for femoral head osteonecrosis between October 1979 and October 1995. Patients who underwent this procedure were at increased risk for proximal femur fractures because of the 16 to 21 mm core drilled through the lateral femoral cortex for removal of the avascular bone and placement of the fibular graft. An ongoing prospective database of patients who underwent this procedure was accessed to determine the incidence of and factors associated with postoperative subtrochanteric femur fractures. Eighteen subtrochanteric fractures occurred for an overall incidence of 2.5%. All fractures occurred through the core decompression site in the lateral femoral cortex. The treatment was nonoperative in seven patients and operative in 11. Fourteen of 18 fractures (77%) healed with an average of 4.1 months until radiographically documented union. Four fractures had nonunions develop, three of which later healed with bone grafting and internal fixation, whereas the fourth eventually required conversion to total hip arthroplasty. Twelve fractures in 251 patients occurred when the weightbearing regimen was touchdown weightbearing for the first 6 weeks and five fractures in 456 patients occurred when the weightbearing regimen was changed to nonweightbearing. The results indicate that nonweightbearing in the immediate postoperative period is associated with the lowest fracture rate.

Potential pitfall of the EndoButton

A clinical and cadaveric example show the EndoButton (Acufex Microsurgical Inc, Mansfield, MA), used for anterior cruciate ligament endoscopic fixation, flipping outside the extensor mechanism or vastus lateralis rather than flipping directly outside the lateral femoral cortex. This pitfall was caused by overdrilling the femoral socket beyond the recommended 6 mm and overadvancing the EndoButton beyond the required depth to flip the EndoButton. Overdrilling the femoral socket to a depth of 10 mm still allows the EndoButton to rest properly on the cortex without soft tissue interposition. Increasing angles of knee flexion at the time of Endobutton placement decrease the safe distance beyond the lateral femoral cortex for flipping without soft tissue interposition. There is also potential to flip the EndoButton within the substance of the vastus lateralis, but the flipping action is blunted and not discrete. Arthroscopy 1998 Jan-Feb;14(1):66-9

Trochanteric union following revision total hip arthroplasty

Ninety-nine patients (106 hips) with a trochanteric osteotomy during revision total hip arthroplasty were evaluated at a minimum of 5 years after surgery. Trochanteric reattachment was done with monofilament cobalt-chromium wires. The influence of the following variables on trochanteric union was examined: a prior trochanteric osteotomy, an existing trochanteric nonunion, trochanteric advancement to the lateral femur, use of vertical (in addition to horizontal) wires through the trochanter, and use of a trochanteric mesh. Overall, union occurred in 92 of the 106 trochanters (87%). Fifty-three of 61 trochanters (86.9%) healed after an initial osteotomy, whereas 34 of 38 (89.5%) healed after a repeat osteotomy. Five of the 7 trochanters with an existing nonunion healed, and 5 of 5 trochanters reattached to a bulk allograft healed. Twenty-nine of 36 trochanters (80.5%) reattached to cancellous bone healed, compared with 58 of 65 (89.2%) that were reattached to the lateral femoral cortex. Ninety percent (83/92) of the trochanters reattached in conjunction with use of a chrome-cobalt mesh healed, compared with 64.3% (9/14) of those without ( P < .05). Of the variables studied, only the use of mesh was statistically significant. Osteotomy through a previously healed trochanter, advancement of the trochanter to cortical bone, existing trochanteric nonunion, trochanteric reattachment to a bulk allograft, and lack of vertical wires for fixation did not adversely affect the likelihood of obtaining trochanteric union.

In vivo observations of hydraulic stiffening in the canine femoral head.

The role that intertrabecular contents and their boundary conditions have on the dynamic mechanical response of canine femoral heads was investigated in vivo. Femoral heads from paired intact hind limbs of canine specimens were subjected to a sinusoidal strain excitation at physiologic frequencies, in the cranio-caudal direction. The fluid boundary conditions for the contralateral limbs were changed by predrilling through the lateral femoral cortex and into the femoral neck. The drilling procedure did not invade the head itself. This femoral head fluid boundary alteration reduced the stiffness by 19 percent for testing at 1 Hz. The results of this study demonstrate that fluid stiffening occurs in vivo as previously observed ex vivo.

Extraarticular Endoscopic Excision of Femoral Head Chondroblastoma

Three femoral head chondroblastomas (one associated with aneurysmal bone cyst) were excised, using a technique of percutaneous extraarticular curettage. Whereas a standard approach to the femoral head lesion requires hip arthrotomy plus a cortical window in the femoral head or neck, the extraarticular technique enters the tumor cavity via a tunnel drilled from the lateral femoral cortex through the medullary canal of the femoral neck. The videoarthroscope assists with visualization during curettage of the cartilage tumor. Bone graft material may be packed into the tumor cavity without fear of subsequent leakage into the joint space. At an average follow-up of 25 months, all three femoral head tumors have healed without recurrence and with no complications related to the approach. The extraarticular endoscopic approach could be used to treat selected benign femoral head or neck lesions other than chondroblastomas.

A MISSING LINK IN THE EVOLUTION OF THR: "DISCOVERY" OF THE LATERAL FEMUR

Using cadaveric studies and mathematical models that include consideration of the iliotibial band (ITB) as a "tension band," the authors have demonstrated that compression loading occurs throughout the entire lateral femoral cortex from the apophyseal line of the greater trochanter to the lateral femoral epicondyle at the knee. This model suggests that the magnitude of this load on the medial and lateral cortices is proportional to the medial displacement of these cortices from the ITB. The authors have further demonstrated that the "tension band" model is more consistent with actual bone morphology and function than existing models and is a strong argument for the incorporation of design concepts such as lateral extensions into total hip arthroplasty femoral components. Such extensions would permit use of lateral femoral cortical bone as an additional base of prosthesis support, distributing loads over a greater area of the proximal femur. This model, therefore, would theoretically reduce the areas of stress concentration in diaphyseal bone and stress shielding of the proximal femur, both of which appear to be deficiencies of present femoral stem designs.

Internal Fixation of Femoral Neck Fractures in the Dog -an in vitro Study

SummaryThe in vitro performances of four recognized fixation methods of femur neck fractures in the dog were evaluated. After a simulated basilar fracture, three multiple pin techniques and a lag screw method were applied to four groups of nine freshly dissected femurs. A standardized force was applied to all specimens as well as five intact femurs and the force-deformation curve and yield points were recorded. Radiographs were taken to determine the mode of failure. The results indicate that the lag screw and three-parallel-pin techniques were significantly stronger than the two-pin methods. The pin techniques failed by either bending and/or slippage, while the lag screw failed by bending and/or pulling in of the screw head into the lateral femoral cortex.An in vitro study, comparing the mechanical performances of four fixation techniques for femoral neck fracture fixation, is presented. The lag screw and three-pin techniques were stronger than the two double-pin techniques. Fixation failure occurred through bending or slippage of the pins, or through bending of the screws or pulling of the screw head into the lateral femoral cortex.

Biomechanical analysis of the dynamic hip screw in the treatment of intertrochanteric fractures

A prospective study was performed in 148 elderly patients (over 60 years old) whose intertrochanteric fractures were caused by moderate trauma. The patients were treated with dynamic hip screws and followed up for at least 2 years (average 34 months). The lag screw was placed as the biomechanical analysis favored. Follow-up showed that the majority achieved good union and were without mechanical failure. The authors conclude that a lag screw should ideally be placed inferiorly toward the medial margin in the frontal plane and centrally in the sagittal plane. The length of the lag screw should be such as to extend from 1.0 cm beneath the subchondral bone to the lateral femoral cortex. At least four cortical screws (piercing the cortex at eight points) should be inserted on the distal femoral fragment.