Implant alignment in knee arthroplasty has been identified as critical factor for a successful outcome. Human error during the registration process for imageless computer navigation knee arthroplasty directly affects component alignment. This cadaveric study aims to define the error in the registration of the landmarks and the resulting error in component alignment. Five fresh frozen cadaveric limbs including the hemipelvis were used for the study. Five surgeons performed the registration process via a medial parapatellar approach five times. In order to identify the gold standard point, the soft tissues were stripped and the registration was repeated by the senior author. Errors are presented as mm or degrees from the gold standard registration. The error range in the registration of the femoral centre in the coronal plane was 6.5mm laterally to 5.0mm medially (mean: −0.1, SD: 2.7). This resulted in a mechanical axis error of 5.2 degrees valgus to 2.9 degrees varus (mean: 0.1, SD: 1.1). In the sagittal plane this error was between −1.8 degrees (extension) and 2.7 degrees (flexion). The error in the calculation of the tibial mechanical axis ranged from −1.0 (valgus) to 2.3 (varus) degrees in the coronal plane and −3.2 degrees of extension to 1.3 degrees of flexion. Finally the error in calculating the transepicondylar axis was −11.2 to 6.3 degrees of internal rotation (mean: −3.2, SD: 3.9). The error in the registration process of the anatomical landmarks can result in significant malalignment of the components. The error range for the mechanical axis of the femur alone can exceed the 3 degree margin that has been previously been associated with implant longevity. The technique during the registration process is of paramount importance for image free computer navigation. Future research should be directed towards simplifying this process and minimizing the effect of human error.
The aim of this study was to assess the risks and benefits of mini-incision TKR. The limited exposure afforded by the small skin incision in the new technique of mini-incision TKR has the potential for increasing the risk of mal-positioning of components. Minor mal-positioning of components has the potential to increase polyethylene wear and may lead to early loosening and poor functioning of the TKR. The literature supports the concept that alignment within +/- 3 degrees of neutral mechanical alignment in the coronal plane is associated with a better outcome. If the mechanical axis falls outside this range it may have up to a 30% failure rate at 10 years. We report the results of 166 mini-incision TKR that have been undertaken in 154 patients (96F; 58M; mean age 72; mean BMI 29; 96% OA) since November 2003. The pre-operative mechanical axis ranged from 8 degrees valgus to 15 degrees varus. Surgery was undertaken with a precise skin incision and a midvastus split approach. Specialised cutting blocks were used to facilitate a smaller incision. The prosthesis inserted was a cemented Zimmer NexGen TKR of either posterior stabilised or cruciate retaining form. Long leg weight bearing alignment radiographs were available in 52% of patients. The mechanical axis was measured in the coronal plane and found to lie within +/- 3 degrees of neutral in 86% of patients. This compares favourably with the current literature which reports the mechanical axis falling within this range in between 72% and 85% of cases. We believe the mini-incision TKR is a safe, reliable and reproducible technique offering substantial savings to the patient and health service without compromising accuracy.
The aim of this paper is to evaluate the Linvatec SE graft tensioner system in obtaining predictable initial tension during ACL reconstruction using hamstring grafts. The gracilis and semitendinosus grafts were tensioned individually prior to fixation distally to a combined tension of 80N. The knees were then cycled through full range of motion and the tension recorded at 90 degrees and in full flexion and extension. Experience on the first 22 patients indicated that 41% required 10 cycles of the knee to remove pre-conditioning and equalise tension at 80N combined, while the remaining 50% required 15 cycles. 90% reached stable tension after 15 cycles. In 54% the tension increased at full extension and graft tension was adjusted to 80N in extension to avoid overconstraining the graft. Twenty-two patients studied following this initial protocol underwent outcome assessment after minimum 6 months. Mean KT1000 arthrometry manual maximum side to side difference was 1.5mm. Femoral fixation was achieved using the Endobutton (Smith and Nephew) and Tibial fixation using the Extralok bioabsorbable screw (Linvatec). A subsequent shortened protocol of initial over-tensioning to 60N and 40N for the semitendinosus and gracilis double bundles respectively, followed by 15 cycles of the knee resulted in stable 80N combined tension with no further drop with more cycling. We conclude that the new tensioner system allows for accurate and predictable initial tension of hamstring reconstructed ACL grafts and that its use can be simplified by using the second technique protocol.
The goal of this study was to evaluate the outcomes from arthroscopic “all inside” meniscal repairs using the FasT-Fix suture system, performed at the Gold Coast and Allamanda Private Hospitals during 2006–2007 40 consecutive meniscal repairs in 36 patients were performed both in isolation and in conjunction with ACL reconstruction. All repairs were performed by the senior author (PG), using an arthroscopic all inside technique with the Fastfix suture anchor system. Patients were assessed at a minimum 6 months follow up, including assessment with the IKDC subjective form. 36 patients underwent a total of 40 meniscal repairs. The average age of the patients was 23.4 years (range 14–42). There were 65% male (26 patients) and 35% female (14 pts). 67.5% (27 menisci) were medial and 32.5% (13 menisci) were lateral repairs. 4 patients underwent bilateral repairs (1 involving 2 different operative dates). 55% (22/40 pts) were right knees and 45% (18/40 pts) were left knees. The average number of FasT-Fix meniscal anchors used was 3.8 (range 1–10). 62.5% (25 pts) underwent concurrent anterior cruciate ligament (ACL) reconstruction. 37.5% (15 pts) were isolated meniscal injuries. 55% (22 pts) had associated chondral surface abnormalities. No Significant complications occurred, including no nerve injuries, infections, or post-operative stiffness. 3 patients underwent subsequent re-operation to resect failed repairs, leaving 37 menisci successfully repaired (92.5%). 5 patients 12.5% described some persistent pain post operation. The average IKDC subjective score for those patients with intact repairs was 91 (62–100). Meniscal repair using an arthroscopic all inside technique provides a safe, reliable and reproducible method of repairing torn menisci, without the need for a further ‘safety incision’ to retrieve and tie sutures. The outcomes from this study indicate that patients demonstrate similar functional results, and low failure rates, similar to other published meniscal repair methods, including the gold standard of inside-out repair.
In perfroming hip resurfacing arthroplasty, concern has been expressed as to the proximity of the femoral neurovascular bundle during the anterior capsulotomy and the risk of damage during this maneuver. We therefore aimed to identify the proximity of the femoral nerve, artery and vein during an anterior capsulotomy done during a hip resurfacing procedure using the posterior approach. A standard posterior approach was performed in 5 fresh frozen cadavic limbs. An anterior incision was then used to measure the distance of the femoral neurovascular structures to the anterior capsule. Measurements from the most posterior aspect of the vessels and nerves to the most anterior aspect of the anterior capsule were taken prior to hip dislocation. The femoral head was then dislocated, and measurements were made with the hip in both flexion and extension. In a separate group of eleven patients that underwent routine MR imaging of the hip, measurements were taken to assess the proximity of the anterior joint capsule to the femoral neurovascular bundle, by a specialist musculoskeletal radiologist who had no prior knowledge of the results obtained during the cadaveric dissection All 5 cadaveric limbs were utilised. 3 were male and 2 were female. The average age was 72.4 years (range 56–84). The patients whom underwent routine MR imaging incorporated 6 males and 5 females with a mean age of 43.7 years (age range 18–64 years). There was no significant difference between the mean distances to the nerve (p=0.21), artery (p=0.21) or vein (p=0.65) between the MR and cadaveric groups. Prior to dislocation the femoral artery and vein were closest to the anterior capsule (mean distance of 21mm) and the femoral nerve was the furthest away (mean distance 25mm). Following dislocation there was a significant increase (25mm to 31mm) in mean distance to the femoral nerve when the superior capsule was cut with the hip in a flexed position (p=0.01) and to the femoral artery in flexion (increase mean distance from 21mm to 35mm) (p<
0.0001) and in extension(increase mean distance from 21mm to 31mm) (p=0.005). When the inferior capsule was cut, there was a significant increase (25mm to 31mm) in mean distance to the femoral nerve and femoral artery when the hip was dislocated and the capsule cut with the hip in flexion (increase mean distance from 21mm to 27mm) (p=0.019) and in extension(increase mean distance from 21mm to 28mm) (p=0.015). This study suggests that the neurovascular structures are relatively well protected during an anterior capsulotomy performed during hip resurfacing. The procedure may be safer if the capsulotomy is performed with the hip dislocated and the hip in a flexed position while cutting the antero-superior aspect and in an extended position while cutting the antero-inferior aspect.
The purpose of this study was to assess the accuracy of clinical assessment compared to imageless computer navigation in determining the amount of fixed flexion during knee arthroplasty. In fourteen cadaver knees, a medial para-patella approach was performed and the navigation anatomy registration process performed. The knees were held in various degrees of flexion with two crossed pins. The degree of flexion was first recorded on the computer and then on lateral radiographs. The cadaver knees were draped as for a knee arthroplasty and nine examiners (three arthroplasty surgeons, three fellows, and three residents) were asked to clinically assess the amount of fixed flexion. Three examiners repeated the process one week later. The mean error from the radiograph in the navigation group was 2.18 degrees (95%CI 2.18+/−0.917) compared to 5.57 degrees (CI 5.57+/− 0.715) in the observer group. The navigation was more consistent with a range of error of only 5.5 degrees (standard deviation 1.59). The observers had a range of error of 18.5 degrees (S.D. = 4.06). When analysing the observers’ error with respect to flexion (+) and extension (−), they tended to under-estimate the amount of knee flexion (median error=−4) whereas the navigation was more evenly distributed (median error=0). The highest correlation was found between navigation and the radiograph r=0.96. The highest observer correlation with the radiograph was a consultant surgeon (r=0.91) and the worst was from a resident (r=0.74). The intra-class correlation coefficient was 0.88 for the three surgeons who repeated the measurements; their mean error was 3.5 degrees with a range of fifteen degrees. The use of computer navigation appears to be more accurate in assessing the degree of knee flexion, with a reduced range of error when compared to clinical assessment. It is therefore less likely to leave the patient with residual fixed flexion after knee arthroplasty.
To assess the accuracy of plain digitised radiographic images for measurement of neck-shaft and stem-shaft angles in hip resurfacing arthroplasty. Fifteen patients having undergone hip resurfacing arthroplasty with the Birmingham Hip Resurfacing (BHR) were selected at random. Digital radiographs were analyzed by three observers. Each observer measured the femoral neck-shaft angles (NSA) of the pre-operative and stem-shaft angles (SSA) of the postoperative radiographs on two separate occasions spanning one week. The effect of femur position on SSA measured by digital radiographs was also analyzed. A BHR prosthesis was cemented into a third generation Sawbone composite femur. Radiographs were taken with the synthetic specimen positioned in varying angles of both flexion and external rotation in increments of 10° ranging from 0° to 90°. The mean intraobserver difference in measured angle was 3.13° (SD 2.37°, 95% CI +/−4.64°) for the NSA group and 1.49° (SD 2.28°, 95% CI +/−4.47°) for the SSA group. The intraclass correlation coefficient for the NSA group was 0.616 and for the SSA group was 0.855. Flexion of the synthetic femur of twenty degrees resulted in a five degree discrepancy in measured SSA and flexion of forty degrees resulted in a thirteen degree discrepancy. External rotation of the synthetic specimen of twenty and forty degrees resulted in a three and nine degree discrepancy in measured SSA, respectively. Patient malposition during radiographic imaging can contribute to erroneous NSA and SSA results. Significant intra- and inter-observer variation was noted in the measurement of neck shaft angle however, variation was less marked for measurement of stem shaft angle.
Alignment of the femoral component during hip resurfacing has been implicated in the early failure of this device. Techniques to facilitate a more accurate placement of the femoral component may help prevent these early failures. We aim to establish whether the use of imageless computer navigation can improve the accuracy in alignment of the femoral component during hip resurfacing. 6 pairs of cadaveric limbs were randomized to the use of computer navigation or standard instrumentation. All hips had radiographs taken prior to the procedure to facilitate accurate templating. All femoral components were planned to be implanted with a stem shaft angle of 135 degrees. The initial guide wire was placed using either the standard jig with a pin placed in the lateral cortex or with the use of an imageless computer navigation system. The femoral head was then prepared in the same fashion for both groups. Following the procedure radiographs were taken to assess the alignment of the femoral component. The mean stem shaft angle in the computer navigation group was 133.3 degrees compared to 127.7 degrees in the standard instrumentation group (p=0.03). The standard instrumentation group had a range of error of 15 degrees with a standard deviation of 4.2 degrees. The computer navigated group had a range of error of only 8 degrees with a standard deviation of 2.9 degrees. Our results demonstrated that the use of standard alignment instrumentation consistently placed the femoral component in a more varus position when compared to the computer navigation group. The computer navigation was also more consistent in its placement of the femoral component when compared to standard instrumentation. We suggest that imageless computer navigation appears to improve the accuracy of alignment of the femoral component during hip resurfacing.
A cadaver study using six pairs of lower limbs was conducted to investigate the accuracy of computer navigation and standard instrumentation for the placement of the Birmingham Hip Resurfacing femoral component. The aim was to place all the femoral components with a stem-shaft angle of 135°. The mean stem-shaft angle obtained in the standard instrumentation group was 127.7° (120° to 132°), compared with 133.3° (131° to 139°) in the computer navigation group (p = 0.03). The scatter obtained with computer-assisted navigation was approximately half that found using the conventional jig. Computer navigation was more accurate and more consistent in its placement of the femoral component than standard instrumentation. We suggest that image-free computer-assisted navigation may have an application in aligning the femoral component during hip resurfacing.
