In recent years, cementless stems have dominated the North American market. There are several categories of cementless stems, but in the past 20 years, the two most popular designs in the United States have been the extensively coated cylindrical cobalt-chrome (Co-Cr) stem and the proximally coated tapered titanium stem, which in recent years has become the most common. The 10 year survival for both stem types has been over 95% with a distinction made on factors other than stem survival, including thigh pain, stress shielding, complications of insertion, and ease of revision. Conventional wisdom holds that proximally coated titanium stems have less stress shielding, less thigh pain, and a higher quality clinical result. Recent studies, however, including randomised clinical trials have found that the incidence of thigh pain and clinical result is essentially equivalent between the stem types, however, there is a modest advantage in terms of stress shielding for a tapered titanium stem over an extensively coated Co-Cr stem. One study utilising pain drawings did establish that if a Co-Cr cylindrical stem was utilised, superior clinical results in terms of pain score and pain drawings were obtained with a fully coated versus a proximally coated stem. In spite of the lack of a clinically proven advantage in randomised trials, tapered titanium stems have been favored because of the occasional occurrence of substantial stress shielding, the increased clinical observation of thigh pain severe enough to warrant surgical intervention, ease of use of shorter tapered stems that involve removal of less trochanteric bone and less risk of fracture both at the trochanter and the diaphysis due to the shorter, and greater ease of insertion through more limited approaches, especially anterior approaches. When tapered stems are utilised, there may be an advantage to a more rectangular stem-cross-section in patients with type C bone. In spite of the numerous clinical advantages of tapered titanium stems, there still remains a role for more extensively coated cylindrical stems in patients that have had prior surgery of the proximal femur, particularly for a hip fracture, which makes proximal fixation, ingrowth, and immediate mechanical stability difficult to assure consistently. Cement fixation should also be considered in these cases. While the marketplace and the clinical evidence strongly support routine use of tapered titanium proximally coated relatively short stems with angled rather than straight proximal lateral geometry in the vast majority of cases, there still remains a role for more extensively coated cylindrical and for specific indications.

INTRODUCTION

The Woodpecker pneumatic broaching system facilitates femoral preparation to achieve optimal primary fixation of the stem in direct anterior hip replacement using a standard operating table. The high-frequency axial impulses of the device reduce excess bone tension, intraoperative femoral fractures and overall operating time. The Woodpecker device provides uniformity and enhanced control while broaching, optimizing cortical contact between the femur and implant and thereby maximizing prosthetic axial stability and longevity. This study aims to describe a single surgeon's experience using the Woodpecker pneumatic broaching system in 649 cases of direct anterior approach (DAA) total hip arthroplasties to determine the device's safety and efficacy.

Abstract

Aims

Femoral bone preparation using compaction technique has been shown to preserve bone and improve implant fixation in animal models. No long-term clinical outcomes are available. There are no significant long-term differences between compaction and broaching techniques for primary total hip arthroplasty (THA) in terms of migration, clinical, and radiological outcomes.

We performed an experimental study to determine the effectiveness of computer assisted robotic bone preparation with regard to primary rotational stability in comparison to hand broaching. Forty-five synthetic femora were prepared by one of two robotic systems (Robodoc n = 12 and CASPAR n = 12) or by one experienced surgeon (n = 21). Seven different types of cementless femoral components were implanted using a standard protocol and measured in a specially designed testing machine with displacement in six degrees of freedom. For each implant at lease 3 measurements were taken for the handbroached and the robotic milled group, respectively. In addition the contact areas between the stems and the bone were visualised.

S-ROM, Antega and ABG stems were lightly more stable in hand broached femora. Osteolock (prepared by both robotic systems) and Vision 2000 stems were more stable in the robot group without changing the movement pattern. G2 and Versys ET performed higher stability with a change to more proximal fixation in the robotic group. Finally four of seven stems had an increase in rotational stability with the robotically milled cavities. The findings highlight the current difficulties in creating a perfect match of robotically milled cavity and stem geometry to achieve enhanced stability. The contact areas differed in some prosthesis in the way of preparation. In some stem geometries area of fixation and the movement pattern of the stem differ with the mode of preparation.

The use of tapered titanium femoral stems has gained in popularity for primary total hip arthroplasty. One of the basic stem designs is a fully grit blast square tapered stem with distal fixation (Zweymuller-type). Another stem design (Muller-type), a proximally porous coated flat wedge stem with proximal fixation is associated with a low but significant perioperative femoral fracture risk. Both of these implant types are inserted with a broach-only technique. We theorize that the Zweymuller-type implant can be inserted safely with pneumatic broaching with a very low fracture risk even when broached by rotating residents with no prior experience.

We prospectively reviewed 300 consecutive hip arthroplasty cases using Zweymuller-type stems from eight different manufacturers implanted using the Woodpecker TM pneumatic broaching system. The series included both THA and hemiarthroplasty cases with a wide range of cortical/canal indexes. Patient age ranged from 14 to 98 (avg. 68). Half of the hip stems were inserted through a posterolateral modified Kocher-Gibson approach, and half through an anterolateral Hardinge approach. Approximately 25 rotating residents who were initially unfamiliar with this broaching technique and stem implant type performed the majority of the procedures. We routinely obtained an intra-operative AP pelvis x-ray to confirm trial implant size, alignment, and adjust the leg lengths.

The overall technique/implant-related perioperative complication rate was 2% (6/300). These included intra-operative femoral fractures(2), post-operative femoral fractures (1), dislocations(3), and deep infections(2). There were no cases of nerve palsy or leg length inequality > 1cm. Rates of post-op blood transfusions and venous thromboembolism were not reviewed for the purposes of this study. Only one of the complications (one deep infection) required exchange of the original femoral component. There was no significant difference in complication rates between type of surgical approach, brand of square tapered stem manufacturer, or experience of the operating surgeon.

We conclude that hip arthroplasty using pneumatically broached, square tapered, cementless distal fixation (Zweymuller-type) hip stems has a low learning curve and can be implanted safely even in very osteoporotic bone. This technique/implant gives the surgeon control of stem anteversion for stability and leg length inequality correction. The incidence of certain perioperative complications can be reduced by using Zweymuller-type stems using pneumatic broaching regardless of approach, implant manufacturer, or surgeon experience. These patients will continue to be followed clinically for implant survivorship.

Introduction. In cementless THA the incidence of intraoperative fracture has been reported to be as high 28% [1]. To mitigate these surgical complications, investigators have explored vibro-acoustic techniques for identifying fracture [2–5]. These methods, however, must be simple, efficient, and robust as well as integrate with workflow and sterility. Early work suggests an energy-based method using inexpensive sensors can detect fracture and appears robust to variability in striking conditions [4–5]. The orthopaedic community is also considering powered impaction as another way to minimize the risk of fracture [6– 8], yet the authors are unaware of attempts to provide sensor feedback perhaps due to challenges from the noise and vibrations generated during powered impaction. Therefore, this study tests the hypothesis that vibration frequency analysis from an accelerometer mounted on a powered impactor coupled to a seated femoral broach can be used to distinguish between intact and fractured bone states. Methods. Two femoral Sawbones (Sawbones AB Europe, SKU 1121) were prepared using standard surgical technique up to a size 4 broach (Summit, Depuy Synthes). One sawbone remained intact, while a calcar fracture approximately 40mm in length was introduced into the other sawbone. Broaching was performed with a commercially available pneumatic broaching system (Woodpecker) for approximately 4 secs per test (40 impactions/sec) with hand-held support. Tests were repeated 3 times for fractured and intact groups as well as a ‘control’ condition with the broach handle in mid-air (ie not inserted into the sawbone). Two accelerometers (PCB M353B18) positioned on the femoral condyle and the Woodpecker impactor captured vibration data from bone-broach-impactor system (Fig1). Frequency analysis from impaction strikes were postprocessed (Labview). A spectrogram and area under FFT (AUFFT) [4] were analysed for comparisons between fractured and intact bone groups using a nested ANOVA. Results. Vibration frequency patterns between respective groups were best observed using an accelerometer positioned on the impaction device rather than on a sawbone (fig1). Qualitative assessment revealed that spectrograms showed no obvious difference for characteristic vibration frequencies between intact and fractured bone groups. A frequency signal at approximately 10kHz was absent for control impactions but present with bone impactions (Fig2). Quantitative assessment revealed AU-FFT was noticeably higher for intact bone groups than fractured bone groups for sampled impactions using a nested experimental design for statistics (p=0.11). Discussion. Our pilot study demonstrates that application of powered impaction combined with vibration frequency analysis has the potential to distinguish between an intact and fractured sawbone in a way that minimises instrumentation footprint and complexity of workflow in OR with a new generation of impaction device targeted at reducing and detecting bone fractures. Further investigation should validate these methods by evaluating the variation with sawbones and simulated bone fractures

Introduction:. Purpose of mini-invasive hip arthroplasty, is least damage to skin and muscles. Unlike Roettinger modification to Watson-Jones, our approach requires no special table or instruments. Besides, direction of skin incision is perpendicular to interval between glutei and tensor muscles, thus called a Crisscross Approach. Incision is at direction of retractors causing less skin damage; and parallel to femur allowing expansion. No tendon or muscles are severed achieving a true inter-muscular non invasive approach. Unlike anterior approach, femoral circumflex vessels and lateral femoral cutaneous nerve are spared. Material and Methods:. 240 prospective patients underwent mini-invasive crisscross technique since December 2006. A standard non-cemented hip was implanted. Previously disrupted hip muscles patients were excluded. In the operating room, patients were secured in a lateral decubitus position with the pelvis flexed at 20°–30° to allow operated leg to extend beyond the table to be placed in a standard plastic bag. The anterior superior iliac spine (ASIS), the greater trochanter (GT) and its tubercle are identified and marked. A line is drawn between ASIS and GT tubercle representing the interval between the glutei and the tensor fascia lata muscles. Another line representing the skin incision is drawn perpendicular. It may be curved a little toward the femur starting two inches inferior and posterior to ipsilateral ASIS extending distally for 3 inches or more for obese or muscular patients. The Crisscross Approach starts with a skin incision being made as above and through the subcutaneous fat identifying the inter-muscular interval between the glutei and the tensor fascia lata. Sharp dissection is made in the connecting fascia only and blunt dissection is needed to separate the two muscles. A branch of the superior gluteal nerve proximally crossing from the glutei to the tensor fascia lata may be encountered but it should not be disturbed as long as blunt dissection is maintained. Curved retractors are placed one above and the other below the femoral neck exposing the anterior capsule. Incision is made in the capsule and the retractors are re-placed to better expose the femoral neck. The appropriate level of neck is osteotomized and the head is extracted as routine. Acetabulum is further exposed by placing the curved retractors at about mid anterior and mid posterior. The final appropriate cup size and orientation is implanted routinely. Before exposing the femoral canal the deep fascia at the junction of the glutei and the vastus lateralis should be incised (about 2–3 inches). This will tremendously help femoral canal exposure. Then the surgeon is positioned anterior, the patient is made fully paralyzed and the table is tilted 20°–30° posteriorly (away from the surgeon). Hip extended 20°–30°, externally rotated to 80°–90° and adducted with a retractor underneath femoral neck and a curved one on greater trochanter to protect the glutei. Leg is allowed to drop in a bag (posteriorly). Canal finder is helpful to avoid going through the cortex Broaching or reaming and final implant insertion as routine. Posterior capsule need not be disturbed; however, the superior and inferior capsule should be detached from the neck to allow better exposure of the femoral canal. Closure starts with one or two stitches in the remainder of the capsule. Then suture deep fascia at the junction of glutei and vastus lateralis with absorbable suture. Finally, subcutaneous fat and skin are closed as routine. Results:. There was no major neurovascular damage or complications related to this exposure. Follow up to a maximum of 75 months revealed no deep infection and no dislocation or fracture. We undersized three stems at the beginning but that did not require re-operation. Surgery time averaged 15 minutes longer but that was reduced as we gained experience. Cup position was navigated and postoperative CT scan confirmed satisfactory cup and stem position. One case that had an undersized prosthesis settling to about half an inch short which required a 3/8 inch insole for the patient to wear. Rehab goals were met after 4–6 sessions in all patients. Patients were allowed to go home on two crutches in 2–3 days. Full weight bearing was allowed in 2–4 weeks. No limping noted at 3 months follow up. Discussion:. Crisscross approach differs by transecting no tendon or muscles, requiring no special table or instruments with incision parallel to femur facilitating expansion and reducing skin damage resulting in true non-invasive approach

The purpose of mini-invasive hip arthroplasty is least damage to skin and muscles. Unlike Roettinger modification to Watson-Jones, our approach requires no special table or instruments. Besides, direction of skin incision is perpendicular to interval between glutei and tensor muscles, thus called a Crisscross Approach. Potentially, a cross shape exposure allows a larger view and therefore a lesser damage to skin and muscles during retraction. Skin incision, being in line with the femur (almost parallel), allows expansion of incision proximally and distally. No tendon or muscles are severed achieving a true inter-muscular minimally invasive approach. After working with 3 cadavers to perfect the technique and with investigation and research board (IRB) approved consent, 40 prospective patients underwent mini-invasive crisscross technique from December 06–June 07 with 6 months follow up. A standard non-cemented hip was implanted. Previously disrupted hip muscles patients were excluded. Patients were positioned in a lateral decubitus with pelvis secured and flexed 20°–30°. Incision started 2 inches inferior and posterior to ipsilateral anterior superior iliac spine (ASIS) extending distally for 3 inches or more for obese or muscular patients. Acetabulum is exposed using curved Hohmann retractors one above and one below femoral neck after excising most of the anterior capsule with releasing the superior and inferior capsule. The femoral neck is osteotomised as routine extracting the femoral head. Then the same curved retractors are placed behind anterior and posterior rim of acetabulum with an optional third curved retractor may be placed at the inferior rim. The acetabulum is reamed with the usual straight reamers and the cup is then implanted as routine. Angled reamers are not necessary as our skin incision is in line with the reamer direction. Femoral neck exposure starts with the surgeon positioned anterior to pelvis. Paralysis of the muscles is confirmed with anesthesiologist and table is tilted 20°–30° posteriorly. Hip is then extended 20°–30°, externally rotated to 80°–90° and adducted with a retractor underneath femoral neck. Another curved retractor is placed gently on greater trochanter to protect glutei. Leg is allowed to drop in a bag. Canal finder and use of box osteotome is helpful to avoid breaching the femoral cortex or varus positioning of the stem. Broaching or reaming and final implant insertion is done as routine. Hip reduction is achieved as routine by reversing the table tilt and bringing the leg forward with traction and internal rotation. 36 out of 38 eligible patients were sent home after their rehab goals were met in 4 therapy sessions (2–3days). Full weight bearing was allowed in 4 weeks. One stem was undersized, two were in slight varus, and total blood loss was less than 5 gm/dl of Haemoglobin at post op day three. No dislocation or complications related to exposure. No neurovascular injury and no re-operation. Surgery time averaged 20 minutes longer mainly at femoral exposure. As experience is gained the time is lessened. Post-operative intravenous morphine pump administration was stopped in 24 hours in 82% of patients after surgery instead of the 48 hour routine. Crisscross approach differs by transecting no tendon or muscles, requiring no special table or instruments with incision that gives more exposure, allows expansion and reduces skin damage resulting in true non-invasive approach. Exposure of the femur was difficult in the first few cases. Tilting the operating table posteriorly, releasing superior and inferior capsule as has been recommended by previous authors helped femoral exposure. Recovery from surgery in terms of rehab sessions and postoperative pain control were improved compared to our previous standard of care. Long term follow up is under current research investigation