Introduction

Management of Vancouver type B1 and C periprosthetic fractures in elderly patients requires fixation and an aim for early mobilisation but many techniques restrict weightbearing due to re-fracture risk. We present the clinical and radiographic outcomes of our technique of total femoral plating (TFP) to allow early weightbearing whilst reducing risk of re-fracture.

Aim

It is unclear if the prevalence of resistance organisms causing (PJI) in total hip/knee arthroplasty is different among North/South American and European countries. Therefore, we sought to compare causative organisms, rates of resistant organisms, and polymicrobial infections in hospitals in North/South America, and Europe.

Objectives

Mechanical wear and corrosion at the head-stem junction of total hip arthroplasties (THAs) (trunnionosis) have been implicated in their early revision, most commonly in metal-on-metal (MOM) hips. We can isolate the role of the head-stem junction as the predominant source of metal release by investigating non-MOM hips; this can help to identify clinically significant volumes of material loss and corrosion from these surfaces.

Introduction

Modular tantalum augments have been introduced to manage severe bone defects in hip and knee revision surgery. The porous surfaces of tantalum augments are intended to enhance osseointegration and a number of studies have documented their excellent biocompatibility. However, the characteristics of tantalum augment osseointegration on human ex vivo specimens from re-revision procedures have not been reported so far.

Introduction

Patellar tracking in total knee replacements has been extensively studied, but little is known about patellar tracking in isolated patellofemoral replacements. We compared patellar tracking and the position of the patellar groove in the natural knee, followed by implantation of the femoral component of a PFR (patella unresurfaced) and after implantation of the femoral & patellar component of the PFR.

Introduction

Several options exist for the treatment of periprosthetic osteolysis in revision knee surgery. We describe our preliminary short-term experiences using trabecular metal (TM) technology in order to fill bony defects either on the femoral or on the tibial side.

Introduction

Mobile-bearing TKRs allow some axial rotation and may provide a more natural patellar movement. The aim was to compare patellar kinematics among the normal knee, fixed-bearing and mobile-bearing TKR.

Unicompartmental knee arthroplasty (UKA) is an increasingly attractive and clinically successful treatment for individuals with isolated medial compartment disease who demand high levels of function. A major challenge with UKA is to place the components accurately so they are mechanically harmonious with the retained joint surfaces, ligaments and capsule. Misalignment of UKA components compromises clinical outcomes and implant longevity. Cobb et al. (JBJS-Br 2006) showed that robot-assisted placement of UKA components was more accurate than traditional techniques, and subsequently that the clinical outcomes were improved. Cobb’s method, however, employed rigid intraoperative stabilization of the bones in a stereotactic frame, which is impractical for routine clinical use. Robotic systems have now advanced to include dynamic bone tracking technologies so that rigid fixation is no longer required. The question is -Do these robotic systems with dynamic bone tracking provide the same accuracy advantages demonstrated with robotic systems with rigidly fixed bones? We compared robot-assisted and traditionally instrumented UKA in six bilateral pairs of cadaver specimens. In all knees, a CT-based preoperative plan was performed to determine the ideal positions and orientations for the implant components. Traditional manual instruments were utilized with a tissue-sparing approach to implant one knee of each pair. A haptic robotic system acting as a virtual cutting guide was used to perform the robot-assisted UKA, again with a tissue-sparing approach. Postoperative CT scans were obtained from all knees, and the 3D placement errors were quantified using 3D-to-3D registration of implant and bone models to the reconstructed CT volumes.

The magnitudes of femoral implant orientation error were significantly smaller for the robot-assisted implants compared to traditionally implanted components (4° vs 11°, p< 0.001), but the magnitudes of femoral placement error did not reach significance (3mm vs. 5mm, p=0.056). The magnitudes of tibial implant placement error were not significantly different (4mm vs. 5mm and 7° vs. 7°, p> 0.05).

Well-placed UKA implants can provide durable and excellent functional results, which is an increasingly attractive option for young and active patients with severe compartmental osteoarthritis who wish not to have or to delay a total knee replacement.

Previous studies have demonstrated significant improvement in implant placement accuracy and clinical results with robot-assisted surgery using rigid bone fixation. This study demonstrates it is possible to achieve significant accuracy improvements with robot-assisted techniques allowing free bone movement. Additional larger trials will be required to determine if these differences are realized in clinical populations.

Measurement of precision in positioning multiple autologous osteochondral transplantation in comparison to the conventional free hand technique.

The articular surfaces of 6 cadaveric condyles (medial – lateral) were used. The knee was referenced by a navigation system (Praxim). The pins carrying the navigation detectors were positioned to the femur and to the tibia. The grafts were taken from the donor side (measurement I) with the special instrument which carried the navigation detectors. The recipient site was prepared and the donor osteochondral grafts were forwarded to the articular surface (II). The same procedure took place without navigation. The articular surface congruity was measured with the probe (measurement III)

The angle of the recipient plug removal (measurement I) with the navigation technique was 3,27° (SD 2,05°; 0°–9°). The conventional technique showed 10,73° (SD 4,96°; 2°–17°). For the recipient plug placement (measurement II) under navigated control a mean angle of 3,6° (SD 1,96°; 1°–9°) was shown, the conventional technique showed results with a mean angle of 10,6° (SD 4,41°; 3°–17°). The mean depth (measurements III) under navigated control was 0,25mm (SD 0,19mm; 0mm–0,6mm). With conventional technique the mean depth was 0,55mm (SD 0,28mm; 0,2mm –1,1mm).

The application of navigation showed that complications like diverging of the grafts leading to breakage or loosening as well as depth mismatch which can lead to grafts sitting over or under the articular surface can be avoided providing better results in comparison to the free hand procedure

Background: Navigation allows for determination of the mechanical axis of the lower extremity. We evaluated the intra- and inter-observer reliability with an image-free navigation system and determined the accuracy of the navigation system to monitor changes in lower limb alignment as compared to alignment measured with a novel 3D CT method.

Methods: A total of 13 cadaver legs were used to evaluate the intra- and inter-observer registration reliability by three observers. Navigated HTOs were then performed on all legs and pre/postoperative values of the varus-valgus angles were recorded. Data were compared to equivalent measures obtained by 3D CT using intra-class correlation coefficients (ICCs).

Results: The ICCs for intra-observer varus-valgus reliability ranged from 0.756 to 0.922, inter-observer reliability was 0.644. ICCs for navigation-CT comparison were 0.784 for varus-valgus angle (pre-op), 0.846 (postop) and 0.873 (delta). Maximum differences in navigation-CT measurements in varus-valgus angle (delta) were 4.5° for all trials. There was poor reliability and accuracy in the axial plane (tibial rotation) as well as fair reliability and accuracy in the sagittal plane (tibial slope).

Conclusion: Image-free navigation is reliable for dynamic monitoring of coronal leg alignment but shows relevant limitations in determination of sagittal and axial plane alignment.

Introduction: Mobile bearing TKRs may allow some axial rotation and also compensate for a slight tibiofemoral rotational mismatch. This is thought to provide better kinematics and a more natural patellar movement. This theoretical advantage has not been verified in clinical studies for the tibiofemoral kinematics. However, little is known about the patellofemoral kinematics of mobile bearing TKRs. The aim was to compare patellar kinematics among the anatomic knee, fixed bearing TKR and mobile bearing TKR.

Methods: Optical computer navigation marker arrays (Brainlab) were attached to the femur, tibia and patella of 9 whole lower extremities (5 fresh cadavers). The trial components of a fixed bearing posterior stabilised TKR (FB) (Sigma PFC, Depuy) were implanted using a tibia first technique. Then the tibia component was changed to a posterior stabilised mobile bearing tibia component (MB) (Sigma RP Stabilised). The patellae were not resurfaced. The knees were moved through a cycle of flexion and extension on a CPM machine. Medial/lateral shift and tilt was measured relative to the patella position in the natural knee at full extension always with soft tissue closure. The path of the trochlea and patellar groove of the femoral component was registered. Values are expressed as mean+/−one standard deviation. Statistical analysis: two tailed paired Student’s T-test.

Results: M/L shift: There was a tendency for the patella to track 2mm more laterally throughout the flexion range with a FB or MB TKR compared to the natural knee, but this did not reach significance.

Tilt: The patella in the natural knee tilted progressively laterally from extension to flexion, plateauing at 50° of flexion (20°: 1.9+/−2.7°, 40°: 5.6+/−5.4°, 60°: 6.2+/−6.4°, 80°:6.5+/−7.3°, 90°: 6.4+/−7.7°). With a FB or MB TKR the patellae also tilted laterally up to 50 degree of flexion, but then started to tilt back medially, reaching the neutral position again at 90°. The patellae of the FB and MB TKRs were significantly more medially tilted at 50° to 90° of flexion compared to the natural knee. But there was no difference between the FB and MB TKRs. (Fixed bearing: 20°: 2.5+/−7.2° p=0.30, 40°: 3.7°+/−6.5° p=0.15, 60°: 3.1+/−5.8° p=0.02, 80°:1.2+/−6.5° p=0.001, 90°: 0.3+/−7.2° p=0.001, Mobile bearing: 20°: 0.3+/−5.5° p=0.27, 40°: 3.6+/−5.2° p=0.08, 60°: 2.1°+/−5.8 p=0.01, 80°: 0.2+/−6.8 p=0.003, 90°: −0.6+/−7.3 p=0.002; vs. natural)

Trochlea position: The centre of the patellar groove of the femur component was more lateral than the trochlea by 2–5mm, it also extended 10mm further proximally.

Conclusion: There are kinematic differences in patellar tracking between the natural and a FB/MB TKR. This may be due to a slightly different position of the patellar groove. The patellar kinematics of the MB TKR is not more natural compared to the FB TKR.

Introduction: Dupuytren’s contracture is a common disease in Northern Europe. Partial fasciectomy is often used to treat the whole spectrum of Dupyutren’s disease, although high recurrence rates have been reported. In our department, the majority of patients are treated by total aponeurectomy, which is defined as the complete removal of palmar tissue. It has been found out that apparently normal-looking aponeurosis can also contain an increased proportion of collagen, which may lead to recurrent disease. Consequently, the perceived advantage of total aponeurectomy over partial aponeurectomy is the potential for a lower recurrence rate as all diseased tissue is potentially removed. Against this background, we have reviewed the effectiveness of total aponeurectomy performed on 61 patients.

Patients and Methods: The group of patients available for review consisted of 51 men and ten women with a mean age of 63.0 (range 42–79 years) and with a mean period of 3.45 years (range 1.03–6.39 years) between operation and review. No patient had follow-up of less than 1 year. At follow-up evaluation hands were examined for nodules, cords and retractions of the skin. The active mobility of the joints was determined with a goniometer and the Jamar hand dynamometer was used to measure grip strength in both hands. Sensitivity was examined by means of two-point-discrimination and the DASH-score was used for the analysis of rehabilitation. Patients were also asked about common risk factors for Dupuytren’s disease.

Results: Post-operative complications including haematoma, seroma or necrosis were found in 13.8% of the patients. Recurrence of contracture occurred in 10.8% of the patients and 4.6% of the operated patients presented with a nerve lesion. Nerve irritation was found in 6.2% of the patients. The mean DASH-score was 3.85 (range 0–52.5). Family pre-disposition was an important risk factor for Dupuytren’s disease with 44.3% of patients having a positive family history.

Conclusion: We suggest that total aponeurectomy is a promising alternative to partial fasciectomy with low risk for recurrent disease and slightly increased risk for a nerve lesion.

Background: Correct ligament balance is a critical factor in both cruciate retaining and substituting total knee arthroplasty (TKA). Due to a lack in current tools, however, little data exists on gap kinematics with the patella is in its anatomical position and with the ligaments tensed. The objective of this study was to quantify the effects of the patellar position and PCL resection on gap kinematics when constant tension is applied to the medial and lateral compartments.

Methods: A novel computer-controlled tensioner was used to measure the medial and lateral gaps in 10 normal knee specimens throughout a full range of motion. Gaps were measured medially and laterally using constant applied forces of 50N, 75N and 100N per side. Gap data were acquired at 0°, 30°, 60°, 90°, 120° of flexion. The test was performed with the patella everted and reduced, and with the PCL intact and resected.

Results: At 90° of flexion:

the mean medial gap was 1.5–2.5mm smaller than the mean lateral gap for all scenarios and forces tested (p< 0.05);

During knee flexion from 30° to 90°, the PCL tended to squeeze the medial compartment by 1–2mm (p< 0.05). Increasing the force from 50N to 100N per side resulted in a mean gap increase of 0.5mm throughout the range of flexion.

Conclusions: Measurement of gap kinematics with a computer-controlled tensioner and a completely reduced patella is feasible. Everting the patella and resecting the PCL both have significant effects on flexion gap balance and symmetry. Knees which are balanced with the patella everted may be post-operatively 1–3mm more lax in flexion than planned. Retaining the PCL may result in asymmetric tightening of the medial gap from 30° to 90°.

Background: Arthroscopic femoral osteoplasties might cause prolonged operative times, restricted intraop-erative overview or insufficient localisation of surgical tools. Computer assisted techniques should improve the precision with an overall accuracy is within 1mm/1°. An automated navigated registration process matching preoperative CT data and intraoperative fluoroscopy, should allow for non-invasive registration for FAI surgery. We evaluated the general precision (I) of the CT and fluoroscopic matching process and (II) the precision of identifying the defined osseous lesions in various anatomical areas.

Material and Methods: Three cadavers (6 hip joints) utilizing a conventional navigation system were used. Before preoperative CT scans, defined osseous lesion (0.5x0.5mm) in the femoral neck, head neck junction, head region were created under fluoroscopic control. Following reference marker fixation, two fluoroscopic images (12 inch c-arm) with 30° angle differences of the hip joint were taken. Automated segmentation including CT-fluoro image fusion by the navigation system enabled a noninvasive registration process Precision of registration process was tested with a straight navigated pointer (1mm tip) trough a lateral arthroscopic portal, during virtual contact to the bone, without arthroscopic control After arthroscopic view was enabled the in vivo distance of pointer tip to bone was measured (I). In vivo real distances between inserted navigated shaver and osseous lesions was done over an anterior hip arthrotomy. Under navigated control, blinded to the situ, placement in the lesions should be done. Distances between shaver tip and osseous lesions were measured with a caliper (II).

Results: The precision for registration (I) was within 0.9mm within the femoral neck (SD 0.24mm; 0.6–1.3mm); 1.2 mm (SD 0.33mm; 0.8–2.0mm) (p> 0.05) for the head neck junction; 2.9 mm (SD 0.57mm; 1.8–3.7mm) for the femoral head (p< 0.001 respectively p< 0.001) Mean offset of the navigated shaver to the lesions (II) was 0.93 mm (SD 0.65mm; 0–2mm). Within the femoral neck a mean accuracy of 0.6mm (SD 0.59mm; 0–1.4mm), the head neck junction 0.8 mm (SD 0.78mm; 0.1–1.5mm), the femoral head 1.3 mm (SD 0.50mm; 0.6–1.7mm) was found (p> 0.05; p> 0.05; p> 0.05).

Conclusion: A combined CT-fluoroscopy matching procedure allows for a reproducible noninvasive registration process for navigated FAI surgery. Precision of the registration process itself is more accurate at the femoral neck and head-neck junction than at the femoral head area. However a navigated identification of osseous lesions was possible within 1mm deviations in all regions.

Background: A navigated 8 in 1 femoral cutting guide for TKA that does not require primary fixation or intramedullary guides was developed. The hypothesis of our study were twofold: 1) the navigation system allows for precise alignment and adjustment of a new femoral 8 in 1 cutting guide with negligible variance in the initially planned vs. achieved implant position; 2) resulting femoral cuts are very accurate without relevant cutting errors.

Material and Methods: We demonstrate our approach with the Universal Knee Instrument (UKI, Precimed Inc. USA), a versatile 8 in 1 TKA guide designed to perform all femoral cuts with a single jig. We integrated an array of “adjustable constraints” into the UKI by machining four threaded holes directly through the template. Adaptation to a navigation system has been performed by integrating the adjustable constraints protocol on the open platform Surgetics Station (PRAXIM-medivision, France), which uses image-free BoneMorphing technology. Based on navigated bone morphing the required preadjustment of the guide was done mechanically, with depth control by mini screws. Testings on 10 cadavers compared the planned vs. achieved positions of the jig before, after fixation, final implant position and planned vs. achieved cutting procedures.

Results: Results revealed for valgus/varus deviations before fixation −0.1°±0.7°, after 0.0°±0.8° (p=0.51), final implant position 0.9°±1.7° (p=0.93). For flexion before fixation −0.3°±1.3° after −0.3°±1.8° (p=0.44), final position 2.9°±2.5° (p=0.65). Distal cut height before fixation 0.0°±0.4°, after 0.1°±0.3° (p=0.61), final position 0.3°±1.0° (p=0.1). Axial rotation before −0.3°±1.1°, after fixation 0.2°±1.4° (p=0.57), final implant position 0.8°±2.7° (p=0.89). Anterior-posterior positions before fixation 0.7°±1.4°, after 1.0°±1.6° (p=0.27), final position 3.4°±1.3° (p=0.13). Highest deviations in the planned vs. actual cut position was found for the posterior cut −3.1°±2.4° in sagittal and anterior cut 0.8°±1.9° in the coronal plane. The highest mean errors in the final implant position where on the order of 3 degrees/mm in flexion and anterior-posterior positioning.

Conclusion: A novel ‘CAS-enabled 8 in 1 jig’ has been developed and validated. The system allows for direct execution of a complex, multi-planar CAS plan with single navigated device. The instrumentation is considerably simplified and eliminates the problems associated with sequential jigs.

Introduction: Image based navigation is able to increase precision and reduce intraoperative radiation time in drilling procedures in orthopeadic trauma indications. Due to specific anatomic conditions and necessary adequate fluoroscopic visualizing, specific indications need intraoperative 3-D fluoroscopy based navigation modalities. This kind of navigation has already been successfully used in several orthopaedic interventions. The complex anatomic structure of the scaphoid, the suggested minimal invasiveness and misplacement rates of the screws make 2-D based fluoroscopic navigation impossible. Missing options for a stable reference marker fixation at the scaphoid or carpus did not allow an intraoperative registration for the navigation. We report about the development of an adequate non invasive fixation technique of the reference marker for navigated interventions and the first implementation of 3-D fluoroscopy based scaphoid screws.

Materials and method: Fixation of the reference marker was achieved by immobilisation of the complete hand and forearm in maximum dorsal extension of the wrist. We used a completely new developed radiolucent hand fixation device (HFD) fixed nonivasively to the carpus and a conventional navigation system (Brainlab, Germany) in combination with 3-D fluoroscopic imaging (Iso-C, Siemens, Germany).

Tests were done on 10 intact specimen and the process included the initial drilling and final placement of an osteosynthetic screw. Postoperative placement was controlled with a 3-D scan. Results concerning a defined optimal screw positioning and drill failures attempts were done by another independent surgeon.

Results: All 3-D scans were done without complications. The multiplanar reconstructions allowed a proper visualisation of the scaphoid in all cases. No additional movement of the fixed extremity occurred during the operation. No registration failures were detected. An optimally defined screw placement in the scaphoid was achieved in 9 cases. Two repeated drill attempts were necessary in one case, another case needed three drill attempts. The scaphoid was never perforated.

Discussion: Our development of a new immobilizing device for the complete hand and forearm allows proper use of 3-D fluoroscopy based navigation at the scaphoid including a placement of an osteosynthetic screw. Further movements of the hand or fingers are intraoperatively only possible after the definite drill placement has been performed.

The 3-D imaging modality allows a direct control of the reduction and screw placement intraoperatively. Our tests did not include simulated fracture conditions, a general use of our new technique can now only be implemented to non displaced fracture types, while clinical and further laboratory tests have to improve our findings for all types of scaphoid fractures.

Introduction: Intraoperative visualisation of anatomic joint line reduction and hardware placement is techniqually demanding, twodimensional c-arm imaging do not always allow acute decision making about remaining articular steps and hardware misplacement. Postoperatively identification of these failures may need extensive revison surgery and is costly. The new mobile Iso-C3D imaging device provides intraoperative multiplanar reconstructions, consequently immediate decision making becomes possible.

Materials and Methods: 250 different joint fractures were intraoperatively scanned with the Iso-C3D (ankle fractures; forefoot, calcaneus; pilon tibiale; tibia plateaus; wrists; spine; pelvic fractures). Multiplanar reconstructions were obtained from 100 fluoroscopic images the Iso-C-3D provides during one automatic scan protocol. Decisions about remaining articular steps and implant misplacements were compared with the knowledge of conventional c-arm images which were done before. If necessary directly intraoperative corrections were performed.

Results: In 43 clinical cases (17%) a direct intraoperative correction resulted in implant change (8%) or correction of reduction (9%), caused by articular steps > 2mm, screw or k-wire misplacement. In all those cases conventional c-arm images did not reveal the significant step or misplacement, correction decision were all based on the Iso-C3D imaging in those cases. In other (9%) significant steps or misplacements were identified in c-arm images and confirmed with the Iso-C3D images.

Discussion: With the new intraoperative three dimensional imaging device a direct introperative idenfication of remaining intraarticular steps and implant misplacements becomes possible. Missed steps and misplacements can be avoided and reduction of operative revison rates might result.

Introduction: The main purpose of this study was to analyze the accuracy of conventional versus navigated open wedge corrective osteotomies of the proximal tibia. Furthermore, the intraoperative radiation dosage and the time of the operative procedure of both groups were compared.

Methods: 20 legs of 11 fresh cadaver (9 male, 2 female, age 35–71 years) were randomly assigned to conventional open wedge high tibial osteotomy (HTO) (n=10) or navigated open wedge HTO (n=10). Two legs had to be excluded because of pre-existing knee injuries. The aim of all corrective operations was to align the mechanical axis to pass through 80% of the tibial plateau (80% Fujisawa line), regardless of the preexisting alignment. The intraoperative mechanical axis was evaluated either by the cable technique for conventional HTO, or by a navigation module for navigated HTO (Medivision, Oberdorf/Switzerland). An angle fixed implant with interlocking screws (Tomofix, Mathys, Bettlach/Switzerland) was used to minimize postoperative loss of correction. Postoperatively, CT-scans were performed and the Fujisawaline and MPTA measured with a computer software for deformity analysis (Med-iCAD) The main outcome parameter was the accuracy of the correction, which was measured by the Fujisawa line. Secondary outcome parameters were the intraoperative radiation measured by the dose area product and the time of the operative procedure. For statistical analysis the standard deviation (S.D.) was calculated and the paired t-test applied.

Results: After conventional HTO, the mechanical axis was intersecting the Fujisawa line at 72.1% of the tibial plateau (range 60.4–82.4%, S.D. 7.2%). In contrast, after navigated HTO the tibia plateau was passed through 79.7% (range 75.5–85.8%, S.D. 3.3%). Thus, the accuracy of the correction was significantly higher after navigated HTO (p=0.020). In addition, the standard deviation of the corrections was significantly lower after navigated HTO (p=0.012). The medial proximal tibia angle (MPTA) increased 7.9° (range: 4.7–12.1°) after conventional HTO and 9.1° (range: 4.6–12.6°) after navigated HTO. The average dose area products of the conventional HTO (49.5 cGy/cm2, range 36.0–81.2 cGy/cm2) and navigated HTO (42.8 cGy/cm2, range 28.3–58.1 cGy/cm2) were comparable (p=0.231). However, navigated HTO elongated the operation time significantly (navigated HTO: 82 min, range 55–98 min; conventional HTO: 59 min, range 47–73 min) (p< 0.001).

Conclusion: Continuous three-dimensional imaging of the axis and of intraoperative tools with the a navigation module significantly improves the accuracy of open wedge osteotomies of the proximal tibia. Prospective clinical studies will show whether the results of this cadaver study can be transferred to the regular clinical use.

Introduction: Movement of the limb during computer aided arthroplasty may cause soft tissue impingement on the reference marker(RM) and consequently alter the spatial relationship between RM and bone with resulting inaccuracies in navigation. The purpose of this study was to investigate the effect of different degrees of soft tissue dissection on the stability of reference markers during limb movement.

Methods: The stability of both one- and two-pin RM systems inserted using three different levels of soft-tissue dissection was analysed in relation to a super-stable RM in fresh cadaver lower limbs. The spatial relationship of the two RMs was analysed using the VectorVision^® system (BrainLAB, Germany) during multiple repetitions of four predefined limb movements. All tests were done with RMs inserted in both the distal-anterior femur and distal-lateral femur.

Results: Analysis of movements of the test RM in relation to the super-stable RM showed that rotations of less than 0.15^o and translations of less than 0.4mm occurred in most test combinations. The combination that showed the greatest instability was when a stab incision was used to insert a pin in the distal/lateral femur (translation 0.73mm+/−0.05, rotation 0.25^o+/− 0.05)(p< 0.001). This instability occurred in both single and double pin RMs(p=0.21).

Conclusions: RM pins can be placed in the anterior distal femur through simple stab incisions without resulting in significant soft tissue impingement during limb movement. If pins are placed in the lateral distal femur through stab incisions, impingement may occur from the fascia lata. Release of the fascia lata 1cm either side of the pin prevents significant impingement. Wide skin incision is unnecessary in any location.

Movement of the limb during computer aided arthroplasty may cause soft tissue impingement on the reference marker(RM) and consequently alter the spatial relationship between RM and bone with resulting inaccuracies in navigation. The purpose of this study was to investigate the effect of different degrees of soft tissue dissection on the stability of reference markers during limb movement.

The stability of both one- and two-pin RM systems inserted using three different levels of soft-tissue dissection was analysed in relation to a super-stable RM in fresh cadaver lower limbs. The spatial relationship of the two RMs was analysed using the VectorVision® system (BrainLAB, Germany) during multiple repetitions of four predefined limb movements. All tests were done with RMs inserted in both the distal-anterior femur and distal-lateral femur.

Analysis of movements of the test RM in relation to the super-stable RM showed that rotations of less than 0.15o and translations of less than 0.4mm occurred in most test combinations. The combination that showed the greatest instability was when a stab incision was used to insert a pin in the distal/lateral femur (translation 0.73mm+/− 0.05, rotation 0.25o+/− 0.05)(p< 0.001). This instability occurred in both single and double pin RMs(p=0.21).

RM pins can be placed in the anterior distal femur through simple stab incisions without resulting in significant soft tissue impingement during limb movement. If pins are placed in the lateral distal femur through stab incisions, impingement may occur from the fascia lata. Release of the fascia lata 1cm either side of the pin prevents significant impingement. Wide skin incision is unnecessary in any location.