Background

Osteotomies around the knee have been used to correct lower limb mal-alignment for over 50 years. The procedure is technically demanding and carries specific risks of neurovascular injury, incorrect planning and execution, and insufficient fixation. In recent years, with the advent of locking plates, fixation techniques have improved significantly but the correct planning and execution of the operation remains difficult. Despite the availability of CT and MRI 3D imaging, surgical planning is still traditionally performed on 2D plain X-rays [1]. Especially with multi-planar deformities, this technique is prone to error. The aim of this clinical pilot study is to evaluate the feasibility of virtual pre-operative three-dimensional planning and correct execution of osteotomies around the knee with the aid of patient specific surgical guides and locking plates.

Summary sentence

The bowing of the femur defines a curvature plane to which the proximal and distal femoral anatomic landmarks have a predictable interrelationship. This plane can be a helpful adjunct for computer navigation to define the pre-operative, non-diseased anatomy of the femur and more particularly the rotational alignment of the femoral component in total knee arthroplasty (TKA).

Introduction

Osteotomies around the knee are traditionally templated on 2D plain X-rays. Results are often inaccurate and inconsistent and multiplanar ostetomies are hard to perform. The aim of this study is to evaluate the feasibility and accuracy of virtual three-dimensional CT-based planning and correct execution of osteotomies around the knee with the aid of patient specific surgical guides and locking plates.

Obtaining a balanced flexion gap with correct femoral component rotation is one of the prerequisites for a successful outcome after total knee replacement (TKR). Different techniques for achieving this have been described. In this study we prospectively compared gap-balancing versus measured resection in terms of reliability and accuracy for femoral component rotation in 96 primary TKRs performed in 96 patients using the Journey system. In 48 patients (18 men and 30 women) with a mean age of 65 years (45 to 85) a tensor device was used to determine rotation. In the second group of 48 patients (14 men and 34 women) with a mean age of 64 years (41 to 86), an ‘adapted’ measured resection technique was used, taking into account the native rotational geometry of the femur as measured on a pre-operative CT scan.

Both groups systematically reproduced a similar external rotation of the femoral component relative to the surgical transepicondylar axis: 2.4° (sd 2.5) in the gap-balancing group and 1.7° (sd 2.1) in the measured resection group (p = 0.134). Both gap-balancing and adapted measured resection techniques proved equally reliable and accurate in determining femoral component rotation after TKR. There was a tendency towards more external rotation in the gap-balancing group, but this difference was not statistically significant (p = 0.134). The number of outliers for our ‘adapted’ measured resection technique was much lower than reported in the literature.

We report the outcome at a minimum of 10 years follow-up for 80 polished tapered stems performed in 53 patients less than 35-years-old with a high risk profile for aseptic loosening. Forty-six prosthesis were inserted for inflammatory hip arthritis and 34 for avascular necrosis. The mean age at surgery was 28 years in the inflammatory arthritis (17–35) and 27 years in the avascular necrosis (15–35) patients. At a mean follow-up of 14.5 years in the inflammatory arthritis group and 14 years in the avascular necrosis group respectively, survivorship of the 80 stems with revision of the femoral component for any reason as an endpoint was 100 % (95 % CI). Re-operation was because of failure of four metal-backed cups, 3 all polyethylene cups and one cementless cup. None of the stems were radiographically loose. All but two femoral components subsided within the cement mantle to a mean of 1.2 mm (0 tot 2.5) at final follow-up. Periarticular osteolysis was noted in 4 femurs in zone 7. This finding was associated with polyethylene wear and was only seen in those hips that needed revision for a metal backed cup loosening. Our findings show that the polished tapered stem has excellent medium-term results when implanted in young patients with high risk factors for aseptic loosening.

In general TKA can be divided into two distinct groups: cruciate retaining and cruciate substituting. The cam and post of the latter system is in fact a mechanical substitution of the intricate posterior cruciate ligament. In our previous work we and many other investigators have focused on the movement of the femoral component relative to the tibial tray. Little information is available about the relative movement between the cam part of the femoral component and the post of the tibial insert. In this study we determine the distance and the changes in distance between the cam of the femoral component and the tibial post during extension, flexion at 90° and full flexion. The secondary purpose is to analyse possible differences between FBPS and MBPS TKA.

Introduction

Autologous chondrocyte implantation presents a viable alternative to microfracture in the repair of damaged articular cartilage of the knee; however, outcomes for patellar lesions have been less encouraging. ChondroCelect (CC) is an innovative, advanced cell therapy product consisting of autologous cartilage cells expanded ex vivo through a highly controlled and consistent manufacturing process.

A comparative kinematic study was carried out on six cadaver limbs, comparing tibiofemoral kinematics in five different conditions: unloaded, under a constant 130 N ankle load with a variable quadriceps load, with and without a constant 50 N medial and lateral hamstrings load. Kinematics were described as translation of the projected centers of the medial (MFT) and lateral femoral condyles (LFT) in the horizontal plane of the tibia, and tibial axial rotation (TR) as a function of flexion angle. In passive conditions, the tibia rotated internally with increasing flexion, to an average of −16° (range −12/−20°, SD 3.0°). Between 0 – 40° flexion, the medial condyle translated forwards 4 mm (range 0.8/5.5 mm, SD 2.5 mm), followed by a gradual posterior translation, totaling −9 mm (range −5.8/−18.5 mm, SD 4.9 mm) between 40° – 140° flexion. The lateral femoral condyle translated posteriorly with increasing flexion completing −25 mm (range −22.6 – −28.2 mm, SD 2.5 mm). Dynamic, loaded measurements were carried out in a knee rig. Under a fixed ankle load of 130 N and variable quadriceps loading, tibial rotation was inverted, mean TR 4.7° (range −3.3°/11.8° SD 5.4°), MFT −0.5 mm (range = −4.3/2.4 mm, SD = 2.4 mm), LFT 3.3 mm (range = −3.6/10.6 mm, SD = 5.1 mm). As compared to the passive condition, all these excursions were significantly different: p=0.015, p=0.013, and p=0.011 for TR, MFT and LFT respectively. Adding medial and lateral hamstrings force of 50N each, reduced TR, MFT and LFT significantly as compared to the passive condition. In general, loading the knee with hamstrings and quadriceps reduces rotation and translation as compared to the passive condition. Lateral hamstring action is more influential on knee kinematics than medial hamstrings action.

High-flexion total knee replacement (TKR) designs have been introduced to improve flexion after TKR. Although the early results of such designs were promising, recent literature has raised concerns about the incidence of early loosening of the femoral component. We compared the minimum force required to cause femoral component loosening for six high-flexion and six conventional TKR designs in a laboratory experiment.

Each TKR design was implanted in a femoral bone model and placed in a loading frame in 135° of flexion. Loosening of the femoral component was induced by moving the tibial component at a constant rate of displacement while maintaining the same angle of flexion. A stereophotogrammetric system registered the relative movement between the femoral component and the underlying bone until loosening occurred.

Compared with high-flexion designs, conventional TKR designs required a significantly higher force before loosening occurred (p < 0.001). High-flexion designs with closed box geometry required significantly higher loosening forces than high-flexion designs with open box geometry (p = 0.0478). The presence of pegs further contributed to the fixation strength of components.

We conclude that high-flexion designs have a greater risk for femoral component loosening than conventional TKR designs. We believe this is attributable to the absence of femoral load sharing between the prosthetic component and the condylar bone during flexion.

Complications involving the patellofemoral joint, caused by malrotation of the femoral component during total knee replacement, are an important cause of persistent pain and failure leading to revision surgery. The aim of this study was to determine and quantify the influence of femoral component malrotation on patellofemoral wear, and to determine whether or not there is a difference in the rate of wear of the patellar component when articulated against oxidised zirconium (OxZr) and cobalt-chrome (CoCr) components. An in vitro method was used to simulate patellar maltracking for both materials. Both rates of wear and changes in height on the patellar articular surface were measured. The mean rates of wear measured were very small compared to standard tibiofemoral wear rates. When data for each femoral component material were pooled, the mean rate of wear was 0.19 mm³/Mcycle (sd 0.21) for OxZr and 0.34 mm³/Mcycle (sd 0.335) for CoCr. The largest change in height on each patella varied from -0.05 mm to -0.33 mm over the different configurations.

The results suggest that patellar maltracking due to an internally rotated femoral component leads to an increased mean patellar wear. Although not statistically significant, the mean wear production may be lower for OxZr than for CoCr components.

Purpose: Precise biomechanical reconstruction of the hip joint by a hip arthroplasty is essential for the success of this procedure. With the increasing use of surface replacement arthroplasty (SRA), there is a need for better understanding of the key factors that influence the anatomical and the biomechanical parameters of the resurfaced hip joint. The goal of this study was to examine the influence of SRA on the vertical and horizontal offset of the hip.

Method: Twenty-one hips from 12 embalmed cadavers were resurfaced with a Birmingham Hip resurfacing. The thickness of the acetabular bone was measured pre- and post-reaming in 6 acetabular zones. Radiographs were taken before and after the procedure with a scaling marker. For statistical analysis, the paired Student’s T-test with a confidence interval of 95% and a significant p-value of p< 0.05 was used.

Results: The mean acetabular bone loss was 3.8 mm, 5.9 mm, 9.3 mm, 10.6 mm, 8.5 mm and 3.6 mm in zones 1 to 6. The “polar length loss” is the cumulative displacement of the femoral and the acetabular articulating surface in zones 2 to 5. This displacement indicates a shortening of the neck plus a medio-cranial displacement of the acetabular articulating surface and was 4.3 mm, 7.5 mm, 9.4 mm and 7.7 mm (zone 2–5). The radiographic center of rotation (COR) was significantly medialised (mean 6.2 mm) and displaced in the cranial direction (mean 6.9 mm) (p< 0.00001). The mean total (femoral plus acetabular) horizontal and vertical offset change was 6.4 mm and 9.5 mm respectively (p< 0.00001). There was a significantly higher vertical offset change in the acetabulum than in the femur (p=0.0006). This resulted in a significantly larger change in vertical than in horizontal offset (p=0,04).

Conclusion: The displacement of the acetabular COR was responsible for 60% of the total vertical and 99% of the total horizontal offset change. The femoral side did not compensate for this displacement. SRA did not restore the biomechanics of the native hip.

Purpose: Plate and cable alone constructs to treat periprosthetic fractures around a well-fixed femoral stem in total hip replacements, have been reported with high failure rates. The aim of this study was to evaluate the results of our surgical treatment algorithm to reliably use lateral plate and cable constructs in these fractures.

Method: One hundred and six periprosthetic fractures in 102 patients were treated between 1996 and 2006. Forty-five fractures were pre-operatively assessed as Vancouver type B1 fractures. The joint was always dislocated and stability of the implant was meticulously evaluated. This led to the identification of nine (20%) unstable stems leaving 36 fractures to be real B1-type fractures. The fracture was considered to be suitable for lateral plate and cable alone fixation if the medial cortex was not comminuted and an anatomical reduction of the medial cortex could be achieved. Twenty-nine B1- and 5 C-type fractures had been treated with a single lateral plate and cable construct. The mean length of follow-up was 43.2 months. The paired Student’s T-test with a confidence interval of 95% and a significant p-value of p< 0.05 was used to compare the pre- and postoperative UCLA hip scores.

Results: Four (12%) patients died within one month from surgery leaving 30 patients for follow-up. Twenty-nine fractures united at a mean of 6.4 months. One B1-type construct failed due to inappropriate proximal fixation. Two fractures united uneventfully with a mean of 8° of varus alignment of the proximal fragment. One patient with a C-type fracture sustained a fracture distal to the tip of the plate. There were three plate infections (8.8%). There was no significant difference between the pre- and post-operative UCLA hip scores (25 versus 23 resp.).

Conclusion: These fractures represent a difficult problem with a high complication rate of 30%. The presented treatment algorithm contributed significantly to the 97% union rate with plate and cable alone constructs that was comparable to the union rates achieved with combined plate and strut graft fixation.

Introduction: High-flexion (HF) TKA designs were introduced in order to achieve greater flexion than with conventional TKA designs. Although early clinical results are promising, recent literature raises concerns about fixation and risk for early loosening of the femoral component during high demanding activities. This study’s aim was to measure the loosening force of the femoral component of several PS-TKA designs in a deep flexion configuration.

Methods: The loosening force of the femoral component of ten contemporary PS-TKAs, including five HF and five conventional designs from the major orthopaedic companies were evaluated. To simulate a deep flexion configuration, each TKA was implanted in a femoral bone model and placed in a loading frame in 135° of flexion, with the tibia vertically. Loosening of the femoral component was induced by raising the tibial insert with constant displacement rate, maintaining the same flexion angle. The resisting force was recorded continuously. A stereo-photogrammetric system registered the relative motion between the femoral component and the bone model. The loosening force was determined when a gap of 2 mm was observed. The influence of pegs on the loosening force was also investigated.

Results: Generally, conventional femoral designs required higher forces before loosening occurred compared to HF designs (p< 0.001). In the group of the HF designs there was a statistically significant difference between the designs (p=0.015) due to the shape of the internal box cut. For some designs, the presence of pegs induced a statistically significant change in loosening force.

Discussion and Conclusion: Several design characteristics of the femoral component can alter its resistance to loosening. In this in vitro study, it was shown that the shape of the internal box cut and the presence of pegs, as well as the geometry of the pegs, are important factors for the loosening force. In the group of the HF components there was a statistically significant difference between the designs with an open and a closed box.

Aim: Component positioning may be adversely affected by minimally invasive approach in total hip replacement due to restricted visualization. Problems with proper alignement are suggested to concern anteversion more than inclination and occur particulary in the lateral position.

Method: 53 patients were enrolled prospectively randomised to each group. First group (standard group, n= 30pts) underwent conventional total hip replacement in supine position and transgluteal approach and second group (MIS group, n= 23pts) underwent THR using minimally invasive anterior approach in lateral decubitus position Every group was operated on by two experienced senior surgeons. Desired cup position was 40°–45°inclination and 15–20° anteversion for the MIS group and 45°inclination and 15 ° anteversion for standard group. Postoperatively all patients had pelvic CT scan. Inclination and anteversion were determined by an independent observer using a 3-D model and planning software, the operative definition was used according to Murray.

Results: Mean inclination/anteversion in the MIS group was 39°(26°–50°)/25°(10°–47°), and 44°(29°–57°)/22°(1°–53°) within the standard group. Standard deviation for inclination was 7° for both groups, and 10° (MIS group) vs 14° (standard group) for anteversion.

The difference in the mean values regarding inclination was greater than would be expected by chance; there was a statistically significant difference (P = 0,010).

Discussion: In general cup positioning in both groups was less steep and more anteverted as presumed. The standard deviation for inclination was the same in both groups, but the standard deviation for anteversion was less in MIS group, that means less outliers regarding anteversion. Cup positioning in minimally invasive total hip replacement is safe compared to traditional approach.

Navigation technique was discussed to equalize the drawback of MIS. However, tools like imageless navigation may further improve the cup position even in traditional approach.

The biomechanics of the patellofemoral joint can become disturbed during total knee replacement by alterations induced by the position and shape of the different prosthetic components. The role of the patella and femoral trochlea has been well studied. We have examined the effect of anterior or posterior positioning of the tibial component on the mechanisms of patellofemoral contact in total knee replacement. The hypothesis was that placing the tibial component more posteriorly would reduce patellofemoral contact stress while providing a more efficient lever arm during extension of the knee.

We studied five different positions of the tibial component using a six degrees of freedom dynamic knee simulator system based on the Oxford rig, while simulating an active knee squat under physiological loading conditions. The patellofemoral contact force decreased at a mean of 2.2% for every millimetre of posterior translation of the tibial component. Anterior positions of the tibial component were associated with elevation of the patellofemoral joint pressure, which was particularly marked in flexion > 90°.

From our results we believe that more posterior positioning of the tibial component in total knee replacement would be beneficial to the patellofemoral joint.

Purpose: A three-year evaluation of long-term clinical efficacy of Characterized Chondrocyte Implantation (CCI) compared to microfracture (MF), in the repair of symptomatic cartilage defects of the femoral condyles at 36 months post-surgery.

Materials and Methods: In a prospective, randomized, controlled, multicenter trial, CCI was compared to MF in patients aged 18–50 years with a single symptomatic ICRS grade III–IV lesion of the knee. Clinical outcome was measured 36 months after surgery by means of the KOOS, VAS for pain and ARS, with a non-inferiority margin preset at 9 % points for KOOS and VAS. Furthermore, response to treatment and progression of knee symptoms were assessed. Treatment failure was monitored throughout the study.

Results: Improvement from baseline was higher in the CCI group (N = 41) compared to the MF group (N = 49) for all clinical outcome parameters. Mean improvement from baseline for Overall KOOS was 22.14 vs. 14.48, respectively, with VAS and ARS scores revealing a similar trend. Responder analysis showed 83% of the patients treated with CCI improving vs. 61% after MF. Additionally, we observed a shift in the proportion of knee symptoms over time (52% vs. 35% of asymptomatic knees at 36 months compared to 2% vs. 8% at baseline in the CCI and MF group respectively). At 36 months, failure rates were low in both groups (n=2 in CCI vs. n=7 in MF).

Conclusions: Previous data have described a superior structural repair after CCI compared to MF at 1 year post-surgery. Continued clinical improvement as well as a favorable responder analysis was demonstrated for CCI compared to MF at 36 months.

Introduction: The Birmingham Hip Resurfacing (BHR) is the most commonly used hip resurfacing for the treatment of hip osteoarthritis. The goal of this study was to evaluate how the surgeon could influence the biomechanical features of the navigated and non-navigated resurfaced proximal femur. METHODS 20 Cadaver hips were resurfaced with a BHR using femoral navigation. The native anteversion and neck shaft angle as indicated by the navigation system were used as a reference. The non-navigated femoral component jig was first placed in the “ideal” position aiming for 10° of valgus and neutral anteversion. The jig was then displaced 5mm in 4 directions. The anteversion and stem shaft angle (SSA) angle were measured for each position using the navigation system. A scaled XR was taken pre- and post-operatively. For statistical analysis, the paired Student’s T-test with a confidence interval of 95% and a significant p-value of p< 0.05 was used.

Results: The centre of rotation (COR) of the navigated resurfaced femur was 3,5 mm significantly (p=0,0006) more distal in the femoral neck than the native COR. This resulted in a 2.1 mm vertical caudal drop (vertical offset) and an average 2.7 mm lateral displacement of the COR (horizontal offset). The same measurements were done with 5° increments of the SSA from 120° to 140°. The vertical offset loss increased non-significantly (1.7 to 2.6 mm). The horizontal offset loss decreased non-significantly (3 to 2.2 mm). The native vertical and horizontal offset could be restored if 5 mm less bone was taken off the femur. The offset loss was significantly increased if 5 mm more bone than the normal reaming had been taken off (p< 0.0001). The “ideal” jig position on the lateral femoral cortex led to an average 137° SSA. Five millimetres of jig displacement on the lateral cortex in either direction did not lead to significant changes in the SSA or anteversion angles relative to the “ideal” position (all p> 0,13). Five millimetres of posterior displacement resulted in an average 139° SSA and 5,8° of anteversion in 95% of hips.

Conclusion: Surgical interventions can significantly change the biomechanics of the hip. Increasing the SSA with a fixed femoral head entry point, as often is done with navigation, does not significantly change the femoral offset. If the surgeon decides to take less bone off the femur, then the offset could be restored and even increased to 1 mm more than the native femur. If due to pathologic changes the bone loss would be increased to 5mm more than the “normal” bone loss, a significant offset loss of > 5 mm could be expected which might lead to detrimental biomechanical effects. The positioning of the jig is subject to surgical errors. The effect of a 5 mm error in either direction does not lead to significant changes in anteversion or SSA. Posterior displacement led to the most reproducible component positioning.

Malrotation of the femoral component is a cause of patellofemoral maltracking after total knee arthroplasty. Its precise effect on the patellofemoral mechanics has not been well quantified. We have developed an in vitro method to measure the influence of patellar maltracking on contact. Maltracking was induced by progressively rotating the femoral component either internally or externally. The contact mechanics were analysed using Tekscan. The results showed that excessive malrotation of the femoral component, both internally and externally, had a significant influence on the mechanics of contact. The contact area decreased with progressive maltracking, with a concomitant increase in contact pressure. The amount of contact area that carries more than the yield stress of ultra-high molecular weight polyethylene significantly increases with progressive maltracking. It is likely that the elevated pressures noted in malrotation could cause accelerated and excessive wear of the patellar button.

The use of plate-and-cable constructs to treat periprosthetic fractures around a well-fixed femoral component in total hip replacements has been reported to have high rates of failure. Our aim was to evaluate the results of a surgical treatment algorithm to use these lateral constructs reliably in Vancouver type-B1 and type-C fractures. The joint was dislocated and the stability of the femoral component was meticulously evaluated in 45 type-B1 fractures. This led to the identification of nine (20%) unstable components. The fracture was considered to be suitable for single plate-and-cable fixation by a direct reduction technique if the integrity of the medial cortex could be restored.

Union was achieved in 29 of 30 fractures (97%) at a mean of 6.4 months (3 to 30) in 29 type-B1 and five type-C fractures. Three patients developed an infection and one construct failed.

Using this algorithm plate-and-cable constructs can be used safely, but indirect reduction with minimal soft-tissue damage could lead to shorter times to union and lower rates of complications.

Purpose: As a one-step surgical procedure, microfracture is frequently considered to be technically easier and associated with less postoperative morbidity than autologous chondrocyte implantation (ACI), which involves both arthrotomy and arthroscopy and therefore safety was assessed in patients with symptomatic cartilage lesions of the knee treated with characterized chondrocyte implantation (CCI) or microfracture.

Methods: CCI (n=57) was compared to microfracture (n=61) in patients with grade III–IV symptomatic cartilage defects of the femoral condyles in a Phase III, prospective, multi-center, randomized, controlled trial. Safety assessments included adverse events (AEs), physical examination, vital signs, hematology and clinical chemistry.

Results: At 18 months post-surgery, similar proportions of patients experienced AEs in the CCI (88%) and microfracture (82%) groups; 67% and 59%, respectively, experienced AEs considered treatment related. The AE profile was generally similar between groups, with no significant difference for hypertrophy, although significantly more CCI-treated patients had joint swelling (19% versus 4.9%; p=0.022) and treatment-related joint crepitation (12% versus 1.6%; p=0.028). Although the proportion of patients with severe AEs was similar for CCI (12%) and microfracture (13%), slightly more microfracture-treated patients experienced serious (life-threatening or requiring hospitalization) AEs (13% versus 8.8%). No patients discontinued due to AEs or died during the study.

Conclusion: Contrary to general opinion, the two-step CCI procedure, involving arthroscopy followed by arthrotomy, has a similar safety profile to that of microfracture, a one-step arthroscopic procedure, for treating cartilage lesions of the knee.