The radiological outcomes of patient-specific instrumentation versus conventional total knee arthroplasty

Purpose

The aim of this study was to investigate the post-operative radiological outcomes of patient-specific instrumentation (PSI) surgery versus conventional total knee arthroplasty (TKA).

Methods

Sixty patients scheduled for a primary TKA were prospectively divided into PSI or conventional technique. Coronal and sagittal radiographic long limb films were taken post-operatively. The accepted values for normal alignment were 180° ± 3° for hip-knee-ankle angle; 90° ± 3° for coronal femoral component angle or coronal tibia component angle; 0° to 3° flexion for sagittal femoral component angle and 0° to 7° posterior slope for sagittal tibia component angle.

Results

For hip-knee-ankle angle, there were 21 % more outliers in the PSI group compared to the conventional group (p = 0.045). Most of these outliers had valgus deformity in the PSI group and varus deformity in the conventional group (p = 0.045). For implant placement, there was no difference in the proportion of outliers between the two groups. There was also no difference in the duration of surgery.

Conclusions

This study showed that PSI surgery is associated with a larger proportion of outliers for lower limb alignment. PSI surgery as an alternative to conventional TKA is not advisable.

Level of evidence

II.     

Joint line reconstruction in medial unicompartmental knee arthroplasty: development and validation of a measurement method

Purpose

Preservation of the joint line in total knee arthroplasty (TKA) has shown to be an important factor for the long-term outcome, especially in revision TKA. For unicompartmental knee arthroplasty (UKA), the role of the joint line has neither been investigated nor is it consciously respected during implantation. Thus, the aim was to establish and validate a standardised measurement method to determine the joint line in UKA.

Methods

As there is no established method to evaluate changes in the joint line radiologically, we introduced two methods and correlated them. The methods were first validated in a cadaver model by a controlled rotational study. Then, the joint line of 29 patients with an UKA (Oxford, Biomet, Bridgend, UK) was determined on pre- and post-operative radiographs. Both methods were tested by intra- and inter-rater reliability.

Results

Both methods showed a good intra- and inter-rater reliability. Furthermore, there was only little bias in agreement between both methods and raters. Measurements of the 29 UKA patients revealed that the joint line was more distally by a mean of 4.4 ± 1.2 mm after surgery.

Conclusions

The study provides for the first time a reliable and standardised measurement tool to determine the changes in the joint line after implantation of an UKA. The instrument should be used in further studies to evaluate the impact of the joint line on the long-term outcome, the load in the two non-replaced knee compartments and on the ligaments.

Level of evidence

Diagnostic study without a universally applied ‘gold’ standard, Level III.     

Total knee arthroplasty for the management of joint destruction in tuberculous arthritis

Purpose

The purpose of this study was to evaluate our experience to clarify the suggestion that there should be a significant disease-free interval before total knee arthroplasty (TKA) and to determine the correct timing of surgery for reconstruction of the joint destruction in patients suffering from tuberculous arthritis.

Methods

Twelve patients with advanced joint destruction and tuberculous arthritis of the knee with recent onset were reviewed in this study. The time interval from our diagnosis of active infection to arthroplasty averaged 4 ± 1.5 months. Histopathology of the biopsy specimens revealing granulomatous lesions, including epithelioid histiocytes surrounded by lymphocytes, confirmed the diagnosis of each patient. A primary knee prosthesis was performed in seven knees. In five knees, there was severe bone loss after the extensive debridement of the entire joint, and thereafter, revision prosthesis was preferred to preserve the joint line. Patients were given post-operative antituberculous treatment for a total of 1 year, whereas for three patients, whose erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) values remained above normal by the sixth month, the chemotherapy was continued for up to 18 months. The Knee Society TKA roentgenographic evaluation and scoring system was used for radiological evaluation of the knees. Clinical evaluation of the knees was done preoperatively and at the time of the most recent follow-up using the American Knee Society Scoring System.

Results

Within the average follow-up period of 6.1 ± 1.8 years, no reactivation of tuberculous infection was found in any of the patients. ESR was normal, less than 20 mm/h, after a mean time of 5.5 ± 2.0 months. The CRP was normal, less than 0.8 mg/dl, after a mean time of 4.6 ± 1.3 months. At the most recent follow-up, the average knee score improved from 32.4 ± 19.4 to 83.4 ± 14.0 points (p < 0.05), and the average function score improved from 33.3 ± 11.9 to 86.6 ± 7.7 points (p < 0.05). Ten knees showed good integrity, and no radiolucent lines were found in the bone–prosthesis interface in relation to any component. Radiolucent lines were apparent on the tibial side in two knees. They were less than 1 mm thick and non-progressive, and clinically, there was no evidence of loosening of the component. Culture specimens were positive for five patients.

Conclusions

TKA is a safe procedure for tuberculous arthritis with recent onset providing symptomatic relief, functional improvement and early return to activity when performed in correct time. A long disease-free interval should not be a prerequisite for arthroplasty. Wide surgical debridement is the mainstay to eradicate the disease, and post-operative antituberculous chemotherapy controls the residual foci.

Level of evidence

IV.     

Knee flexion after total knee arthroplasty reduces blood loss

Purpose

Extensive blood loss after total knee arthroplasty (TKA) may be a potential problem since it leads to anaemia, increased need for transfusion and prolonged hospitalization. Aim of this study was to investigate the effects of postoperative knee flexion after TKA on blood loss and the need for transfusion.

Methods

One hundred consecutive patients undergoing primary TKA from 2012 to 2013 were randomizely divided into two groups. In one group, the knee was extended for the first 6 h after surgery, whereas in the other was flexed at 90° for the same time. Two doses of endovenous tranexamic acid were administered in all subjects. Patients were homogeneous for all the possible confounding factors.

Results

Calculated blood loss was 846 ± 197 (ml) in the flexion group and 1,242 ± 228 (ml) in the extension group (p < 0.05). Drop of haemoglobin levels at 24 h in the study group and the control group was 1.9 ± 0.8 (g/dl) and 3.0 ± 0.5 (g/dl), respectively (p < 0.01). Drop of haematocrit at 24 h was 4.5 ± 0.2 (%) in the flexion group and 6.7 ± 0.3 (%) in the extension group (p < 0.05). Blood transfusion was necessary in 5 patients in the control group and was not necessary in any patient of the study group. Average knee flexion at day 7 was 105° ± 4° in the flexion group and 98° ± 7° in the extension group.

Conclusion

Knee flexion at 90° after TKA, associated with the intraoperative use of tranexamic, acid is an effective method to reduce blood loss and the need for blood transfusion. The routine use of the present protocol is effective in reducing social costs and length of hospitalization of TKA procedures.

Level of evidence

Prospective comparative study, Level I.     

Radiographic accuracy in TKA with a CT-based patient-specific cutting block technique

Purpose

Patient-specific instrumentation (PSI) technology for the implantation of total knee arthroplasty (TKA) has a rising interest in the orthopaedic community. Data of PSI are controversially discussed. The hypothesis of this paper is that the radiological accuracy of CT-based PSI is similar to the one of navigated TKA published in the literature.

Methods

Since 2010, all 301 consecutively performed PSI TKAs (GMK MyKnee©) were included in this study. The radiological assessment consisted in a preoperative and postoperative standard X-ray and long-standing X-ray. Changes from the planned to the definitively implanted component size were documented. Postoperative analysis included limb alignment and position of femoral and tibial components (for varus/valgus and flexion or tibial slope).

Results

The postoperative average hip–knee–ankle angle was 180.1° ± 2.0°. In the frontal plane a total of 12.4 % of outliers >3°, for the tibial components 4.1 % of outliers >3° and for the femoral components 4.8 % of outliers >3° were measured. A total of 12.3 % of outliers for posterior tibial slope and 9 % of outliers >3° for the femoral flexion were noted. 10.8 % of the 602 planned size components were adapted intraoperatively.

Conclusion

Although it is still unknown which limb axis is the correct one for the best clinical result, a technology providing the aimed axis in a most precise way should be chosen. Comparing the outcome of the current study with the data from the literature, there does not seem to be any difference compared to computer-assisted surgery.

Level of evidence

IV.     

No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament

Purpose

Anterior cruciate ligament deficiency (ACLD) has been considered a contraindication for Oxford unicompartmental knee arthroplasty (UKA) because of the reported higher incidence of failure when implanted in ACLD knees. However, given the potential advantages of UKA over total knee arthroplasty (TKA), we have performed UKA in a limited number of patients with ACL deficiency and end-stage medial compartment osteoarthritis (OA) over the past 11 years. The primary aim of this study was to establish the clinical outcome of this cohort; the secondary aim was to compare both clinical and radiographic data with a matched cohort of ACL-intact (ACLI) patients who have undergone UKA for anteromedial OA.

Methods

This retrospective observational study describes the clinical and radiological outcome in 46 medial Oxford UKAs implanted in 42 consecutive patients with ACL deficiency and concomitant symptomatic medial compartment OA at mean follow-up of 5 years. It also compares the outcomes with a matched cohort of UKA patients with an intact ACL (ACLI group).

Results

At the time of last follow-up, there was no significant difference in clinical results or survivorship between the two groups in this study.

Conclusion

The successful short-term results of the ACLD group suggest ACL deficiency may not always be a contraindication to Oxford UKA as previously thought. Until long-term data is available, however, we maintain our recommendation that ACLD be considered a contraindication.

Level of evidence

III.     

Difference in knee rotation between total and unicompartmental knee arthroplasties during stair climbing

Purpose

The purpose of this study was to compare knee kinematics during stair walking in patients with simultaneous total knee arthroplasty (TKA) and unicompartmental knee arthroplasties (UKA). It was hypothesized that UKA would reproduce more normalized knee kinematics than TKA during stair ascent and descent.

Methods

Six patients who received UKA in one knee and TKA in the other knee were included in the study. For this study, a four-step staircase was assembled with two force platforms being positioned at the centre of the second and third steps. Each patient was attached with 16 reflective markers at both lower extremities and was asked to perform five roundtrip trials of stair climbing. Kinematic parameters including stance duration, knee angle, vertical ground reaction force (GRF), joint reaction force, and moments were obtained and analysed using a10-camera motion system (VICON, Oxford, UK). Nonparametric Friedman test was used to compare the results between two arthroplasty methods and between stair ascent and descent.

Results

Compared to TKA, UKA knees exhibited significantly greater degree of rotation in transverse planes (5.0 degrees during ascent and 6.0 degrees during descent on average), but showed no difference in terms of the other parameters. When comparing the results during stair ascent with descent, overall greater knee angle, vertical GRF, joint reaction force, and moment were observed during stair descent.

Conclusions

Both UKA and TKA knees have shown overall similar knee kinematics, though UKA knee may allow greater degree of rotation freedom, which resembles normal knee kinematics during stair walking.

Level of evidence

Case–control study, Level III.     

Is bicompartmental knee arthroplasty more favourable to knee muscle strength and physical performance compared to total knee arthroplasty?

Purpose

Bicompartmental knee arthroplasty features bone and ligament sparing as unicompartmental knee arthroplasty and is presumably better in the recovery of muscle strength and function compared to total knee arthroplasty (TKA) though not previously reported in the literature. The aim of the study was to compare isokinetic knee muscle strength and physical performance in patients who underwent either bicompartmental knee arthroplasty or TKA.

Methods

Each of 24 patients (31 knees) was prospectively examined preoperatively, at 6 and 12 months after each surgery. Isokinetic knee extensor and flexor strength as well as position sense were measured using the Biodex system. Timed up and go test, stair climbing test, and the 6-min walk test were used to assess physical performance. The results of each group were also compared with those from the corresponding healthy control, respectively.

Results

Demography showed significant difference in the mean age between bicompartment (54.8 ± 5.6 years) and TKA groups (65.7 ± 6.7 years). Comparing between the two groups, knee extensor and flexor torque, hamstring/Quadriceps ratio, position sense, and physical performance were not significantly different preoperatively, at 6 and 12 months after surgery. In intra-group analysis, muscle strength and position sense at each time point were not different in both groups. In physical performance, both groups resulted in improvement in the 6-min walk test, and only TKA group showed enhancement in stair climbing test.

Conclusions

Although theoretically plausible, bicompartmental knee arthroplasty was not superior in knee muscle strength and physical performance at 1 year compared with total knee arthroplasty.

Level of evidence

II.     

The comparative efficacies of intra-articular and IV tranexamic acid for reducing blood loss during total knee arthroplasty

Purpose

Reduction in blood loss during surgery stabilizes hemodynamic status and aids in recovery after total knee arthroplasty (TKA). In this study, the authors examined whether different administration routes of tranexamic acid (TNA) might affect the amount of blood loss after TKA.

Methods

A total of 150 patients were prospectively allocated to each of the three groups (intravenous, intra-articular, and placebo group) and underwent unilateral TKA. During closing the operative wound, TNA (1.5 g mixed in 100 cc of saline) was administered intravenously or intra-articularly according to the enrolled group, and an equivalent volume of normal saline was administered into the knee joint cavity and intravenously in the placebo group, respectively. The amount of blood loss and transfusion, and changes in haemoglobin levels were documented accordingly.

Results

The mean blood loss in the intravenous, intra-articular, and placebo groups were 528 ± 227, 426 ± 197, and 833 ± 412 ml, respectively. About 66 % (intravenous), 80 % (intra-articular), and 6 % (placebo) of each group did not require transfusion for any reason, and the mean amount of transfusion was 273.6, 129.6, and 920.8 ml, respectively. Preoperative haemoglobin values decreased by 1.6 ± 0.8, 1.8 ± 0.8, and 2.0 ± 0.9 mg/dl, respectively.

Conclusion

Compared to intravenous administration, intra-articular administration of TNA seems to be more effective in terms of reducing blood loss and transfusion frequency. TNA may improve the general conditions of patients given TKA by maintaining a hemodynamically stable state, aiding in recovery, and reducing the chance of transfusion-associated side effects and complications.

Level of evidence

II.     

The Rotaglide mobile-bearing total knee arthroplasty: no difference between cemented and hybrid implantation

Purpose

The optimal fixation of the Rotaglide total knee arthroplasty’s (TKA) components is controversial. It is hypothesized that the hybrid fixation (cementless femoral component) in a mobile-bearing TKA system might cause increased rate of loosening—especially in the femoral part—and finally failure of the arthroplasty. Consequently, the aim of this study was to compare the survival and revision rates and also the clinical and radiological outcomes of the cemented and hybrid fixation of the Rotaglide TKA.

Methods

One hundred patients, who underwent TKA with the Rotaglide prosthesis, were randomly placed in two groups. In the first group, the prosthesis was cemented, and in the second group, the hybrid technique was used. Revision and mortality rates were compared after 8–12 years of follow-up. Knee and Osteoarthritis Outcome Score (KOOS) questionnaire and the Knee Society Roentgenographic Evaluation and Scoring System were used to demonstrate clinical and radiographic differences.

Results

There were no statistically significant differences in revision (n.s.) or mortality (n.s.) rates between the two treatment arms. The clinical outcome at the time of last follow-up (mean 9.5 years, SD ±1.4) ranged from very good to excellent (77.8 ± 17.5 for the cemented group and 77.2 ± 20.4 for the hybrid group). No statistically significant differences in all KOOS subscales. Radiographs showed no significant difference in prosthesis alignment and no evidence of loosening between groups.

Conclusion

The hypothesis that the hybrid fixation in a mobile-bearing TKA system might cause increased rate of loosening and finally failure of the arthroplasty was not confirmed. The fixation technique (cemented or hybrid) had no influence on the prosthesis’s survivorship, and also on mortality rates, clinical and radiographic outcomes in a mean follow-up time of 9.5 ± 1.4 years. The Rotaglide TKA is a safe and reliable prosthesis regardless the fixation technique.

Level of evidence

Prospective comparative study, II.     

Assessment of accuracy of robotically assisted unicompartmental arthroplasty

Purpose

The purpose of this study was to analyse the accuracy of component placement during unicompartmental knee arthroplasty (UKA) using a robotic-assisted system.

Methods

Two hundred and six patients (232 knees) who underwent medial robotic-assisted UKA were retrospectively studied. Femoral and tibial sagittal and coronal alignments were measured in the post-operative radiographs and were compared with the equivalent measurements collected during the intra-operative period by the robotic system. Mismatch between pre-planning and post-operative radiography was assessed against accuracy of the prosthesis insertion.

Results

Robotic-assisted surgery for medial UKA resulted in an average difference of 2.2° ± 1.7° to 3.6° ± 3.3° depending on the component and radiographic view between the intra-operatively planned and post-operative measurements. Mismatch between pre-planning and post-operative radiography (inaccuracy) was related to improper cementing technique of the prosthesis in all measurements (except for tibial sagittal axis) rather than wrong bony cuts performed by the robotic arm.

Conclusion

Robotic-assisted medial UKA results in accurate prosthesis position. Inaccuracy may be attributed to suboptimal cementing technique.

Level of evidence

Comparative retrospective study, Level III.     

Dutch translation of the Kujala Anterior Knee Pain Scale and validation in patients after knee arthroplasty

Purpose

To translate and validate the Kujala Anterior Knee Pain Scale (AKPS) in patients who have undergone total knee arthroplasty (TKA) or unicompartmental knee arthroplasty (UKA) and evaluate the internal consistency, construct validity and ceiling or floor effect.

Methods

After standard forward and backward translation was performed, 302 patients who have received a TKA or UKA filled out the AKPS together with Hospital for Special Surgery (HSS) patella score, visual analogue score (VAS) for pain, the Oxford 12-item questionnaire and the SF-36 at follow-up. The internal consistency was tested using Cronbach’s α coefficient. The construct validity was assessed using Spearman’s rank correlation (R) to test for correlations between the AKPS and VAS HSS, HSS patella score, VAS month, Oxford 12-item questionnaire and SF-36 subscales. Ceiling or floor effects are given in percentage of patients giving a maximum or minimum score.

Results

The internal reliability of the AKPS is acceptable with a Cronbach’s α of 0.81 in patients after TKA or UKA. A high correlation was found between the AKPS and the Oxford 12-item questionnaire (R = 0.81). Moderate correlations were found with the VAS month (R = 0.63), HSS patella score (R = 0.51) and SF-36 subscales physical functioning (R = 0.59), role-physical (R = 0.59), bodily pain (R = 0.57). Other correlations were poor, therefore indicating a good convergent and divergent validity. Ceiling effects were observed for the HSS patella score (31 %), VAS HSS (51 %), VAS pain (19 %), SF36-RP (46 %), SF36-RE (80 %) and SF36-BP (24 %). No ceiling or floor effect was found for the AKPS, Oxford 12-item and the other SF36 domains.

Conclusions

The AKPS appears to be reliable and valid in patients after knee arthroplasty, with no ceiling and floor effects, and can be used to assess anterior knee pain in patient who underwent joint replacement surgery.

Level of evidence

Diagnostic study, Level I.     

Patient-specific instruments: industry’s innovation with a surgeon’s interest

Purpose

The aim of this study was (1) to survey the orthopaedic companies about the volume of patient-specific instruments (PSI) used in Europe and worldwide; (2) to survey a group of knee arthroplasty surgeons on their acceptance of PSI and finally; (3) to survey a medico-legal expert on PSI-related issues.

Methods

Seven orthopaedic implant manufacturers were contacted to obtain their sales figures (in volume) of PSI in Europe and worldwide for the 2011 and 2012 period. During the Open Meeting of the Belgian Knee Society, a survey by a direct voting system was submitted to a selection of knee surgeons. Finally, a number of medico-legal ‘PSI-related’ questions were submitted to an adult reconstruction surgeon/legal expert.

Results

The total volume, for all contacted companies, of PSI in Europe for 2012 was 17,515 total knee arthroplasty (TKA) and 82,556 TKA worldwide. Biomet (Warsaw, USA) was the number one in volume, both in Europe as worldwide with their Signature system. Biomet represented 27 % of the market share in PSI worldwide. Stryker preferred not to reply to the survey because of the FDA class 1 recall on ShapeMatch cutting guides. Eighty per cent of the Belgian knee surgeons expressed a great interest in PSI and especially, for 58 % of them, if it would increase their surgical accuracy. They valued it even more in unicompartmental arthroplasty, and 55 % was ready to use single-use instruments. Surprisingly, 47 % of surgeons thought it was the company’s responsibility if something goes wrong with a PSI-assisted case. The medico-legal expert concluded that PSI is a complex process that exposes surgeons to new risks in case of failure and stated that companies should not produce surgical guides without validation of the planning by the surgeon.

Conclusion

Patient-specific instruments is of great interest if it can proof to increase the surgical accuracy in knee arthroplasty to the level surgeons are expecting and if in the same time it would make the surgical process more efficient.

Level of evidence

V.     

Alteration in skin sensation following knee arthroplasty and its impact on kneeling ability: a comparison of three common surgical incisions

Purpose

Disturbance in skin sensation is a recognised, often unpleasant consequence of knee replacement for many patients and may affect function especially kneeling. The aim of this study was to compare post-operative changes in skin sensation following total (TKA) and unicompartmental knee (UKA) arthroplasties using three different incision types and its effect on kneeling ability.

Methods

Skin sensation was recorded using a purpose-designed grid over the front of the knee in 72 patients (78 knees) following knee arthroplasty. Surface area of sensory change, length of incision, and kneeling ability were recorded and compared between three different types of incision; long antero-medial and midline for TKA, and short medial for UKA.

Results

The average length of the long antero-medial incision was 19?±?5?cm with an average area of sensory alteration of 88?±?56?cm². The average length of the midline incision was 18?±?3?cm with an average area of sensory alteration of 57?±?52?cm². The short medial incision used for UKA averaged 11?±?3?cm in length with an average area of sensory alteration of 54?±?45?cm². Long antero-medial produced a significantly greater area of sensory alteration than standard short medial (P?=?0.017), but not the midline incision. There was a significant positive correlation of incision length with reduced sensation. Patients unable to kneel demonstrated a significantly larger area of hypersensitivity than patients who could kneel (P?=?0.002).

Conclusions

Increased length of incision results in a greater surface area of sensory change in the front of the knee. This finding was greatest in the long antero-medial incisions used in TKA. The inability to kneel following knee arthroplasty is associated with increased area of hypersensitivity of the anterior knee.

Level of evidence

Prospective comparative study, Level II.     

No influence of coronal laxity and alignment on lift-off after well-balanced and aligned total knee arthroplasty

Purpose

In vivo fluoroscopic analyses have revealed the kinematics after total knee arthroplasty (TKA), including femoral condylar lift-off. This study asked whether differences in static varus–valgus laxity or coronal limb alignment after TKA affect lift-off under weight-bearing conditions. It was hypothesised that there is a correlation between coronal laxity or alignment and lift-off during walking.

Methods

The current study analysed nineteen subjects undergoing cruciate-retaining TKA performed by the measured resection technique. The varus–valgus laxity at knee extension was measured using a 150 N stress radiograph. The mechanical axis was measured using a full-standing radiograph. Continuous radiological images were taken while the subject walked on a treadmill, and the images during single-leg stance were analysed to determine the lift-off using a 3D-to-2D image-to-model registration technique.

Results

The average angle in varus/valgus stress was 6.8 ± 1.8°/6.6 ± 2.1°. No statistically significant differences were observed between the varus and valgus laxity. The average amount of lift-off was 0.7 ± 0.4 mm. The static varus–valgus laxity (n. s.) or the differences in the laxities (n. s.) on the stress radiograph did not influence lift-off. The weight-bearing ratio was achieved within the middle third of the knee in 90 % of subjects. Two outliers with valgus alignment (68 ± 1 %) demonstrated no significant difference in lift-off in comparison with the majority of the subjects (46 ± 9 %).

Conclusion

The static coronal laxity and alignment did not influence the lift-off under dynamic weight-bearing conditions after well-balanced and aligned cruciate-retaining TKA. Measured resection technique can produce sufficient coronal stability and alignment without significant lift-off during walking.

Level of evidence

IV.     

The difference between weight-bearing and non-weight-bearing alignment in patient-specific instrumentation planning

Purpose

Retrospective study to analyse the difference between weight-bearing and non-weight-bearing alignment in osteoarthritic knees planned for patient-specific instrumented (PSI) total knee arthroplasty (TKA). The aim of the study is to observe whether a difference in alignment can be linked to arthritis staging or zone mechanical axis.

Methods

Full-leg standing radiographs and non-weight-bearing MRI of the whole leg were compared for hip–knee–ankle (HKA) angle, measured according to Moreland criteria, in seventy osteoarthritic patients. Kellgren–Lawrence (KL) staging and classification according to zone mechanical axis with Kennedy zones was done.

Results

A mean preoperative HKA angle on standing radiographs of 176.4° ± 7.2° was measured compared to 176.4° ± 6.9° for the MRI whole-leg HKA angle. A difference of 0°–1° was observed in 54 % of patients when comparing the weight-bearing with the non-weight-bearing HKA angle. Twenty-three per cent had a difference of 2° and another 23 % a difference of 3° or more. In female patients, the dynamic load pattern of weight-bearing increases the HKA angle due to convex side soft tissue laxity both in varus and valgus knees. More important differences were observed in the KL stage 3 and 4 patients (P < 0.05) and with a load-bearing axis outside of the articular surface (P < 0.05).

Conclusion

Surgeons should be aware that there is a difference between weight-bearing and non-weight-bearing alignment in patients with Kellgren–Lawrence 3 and 4 with a load-bearing axis outside of the articular surface (Kennedy 0 or 1 or 5). According to this study, these changes seem related to the amount of articular wear and the load-bearing axis. This is important for the preoperative planning process in PSI-assisted TKA. More concave side ligamentous release or more constraint can be necessary than imagined based on the PSI alignment result. Full-leg standing radiographs should be performed for PSI-assisted TKAs to analyse the position of the load-bearing axis.

Level of evidence

IV.     

Muscle activity around the knee and gait performance in unicompartmental knee arthroplasty patients: a comparative study on fixed- and mobile-bearing designs

Purpose

Unicompartmental knee arthroplasty (UKA) offers clinical and functional advantages over total knee arthroplasty. The aim of this study was to compare the functional recovery of patients with mobile UKA versus fixed-bearing designs by state-of-the-art gait analysis and, in particular, by assessing muscular activity.

Methods

Ten patients with the Oxford (mobile bearing) and ten patients with Optetrak (fixed bearing) UKA were evaluated at a minimum follow-up of 1?year post-operatively by gait analysis, which includes the main time–distance parameters, kinematics and kinetics of the replaced knee, and muscular activity of the main relevant muscles. Twenty healthy young subjects were used as controls.

Results

The mean International Knee Society score was 92.7?±?11.2 for all 20 UKA knees; for the Oxford UKA, it was 94.1?±?9.5; and for the Optetrak UKA, it was 91.5?±?12.9, although follow-up was significantly lower for the latter. Time–distance parameters showed a slower gait in both groups compared with that of controls, and the Oxford group had values closer to the controls. Knee joint flexion was similar to that of controls at initial contact and loading response with no differences between groups. In all patients, the joint moments were smaller to that of controls. Residual abnormalities such as the prolonged rectus femoris activity were present in both designs, and the only difference distinguishing the Optetrak group from the others was the combined co-contraction of the hamstrings.

Conclusions

A good restoration of gait was achieved by most unicompartmental knee patients independently of the UKA design, although some abnormalities persisted in muscle activity around the knee.

Level of evidence

Retrospective comparative study, Level III.     

Patellar tilt and thickness do not influence postoperative flexion in a high-flex design total knee arthroplasty

Purpose

The purpose of this short-term study was to determine whether patellar thickness and tilt influence the postoperative flexion in a high-flex design total knee arthroplasty (TKA).

Methods

Between 2007 and 2009, 106 patients underwent surgery for TKA using rotating platform flex prosthesis (DePuy, Warsaw, Ind). All of them were suffering from end-stage osteoarthritis. All patients were evaluated preoperatively and at 12 months of follow-up. Maximum active, non-weight-bearing flexion was the primary outcome parameter. Standard standing antero-posterior and lateral weight-bearing radiographs were made. The patellofemoral joints were evaluated in skyline views taken with the knees at approximately 60° of flexion. Patellar thickness, patellar tilt, Caton–Deschamps indices and lower limb alignment were measured.

Results

The mean flexion observed before surgery was 125° ± 15° and after 1 year was 128° ± 13°. The mean patellar thickness preoperatively was 24.5 ± 2.9 and 25.8 ± 3.2 mm at 12 months after surgery. The mean patellar tilt before the procedure was 2.9° ± 4.1° and after 12 months of follow-up was ?0.8° ± 5.0°. The mean preoperative hip-knee-ankle was 2.6° ± 6.2°. No significant correlation was found between postoperative patellar tilt and thickness and postoperative flexion (n.s.).

Conclusions

Patellar tilt and thickness after TKA are factors that depend on the surgery. The resection of the patella can influence both patellar thickness and patellar tilt. By developing adequate surgical instruments, it would be possible to avoid the occurrence of an exaggerated patellar tilt or a major difference in patellar thickness. However, these two factors did not seem to influence the postoperative flexion in a high-flex design TKA, which can be seen as one of the most important outcome factors after TKA.

Level of evidence

IV.     

Revision total knee arthroplasty with varus–valgus constrained prosthesis versus posterior stabilized prosthesis

Purpose

The aims of this retrospective study were to provide the basis for the choice of prosthesis in revision total knee arthroplasty (TKA) and to evaluate the outcome with varus–valgus constrained prosthesis compared with posterior stabilized (PS) prosthesis.

Methods

One hundred and five patients (121 knees) received revision TKA; of which thirty-seven patients (42 knees) received PS prosthesis and sixty-eight patients (79 knees) received varus–valgus constrained prosthesis. The mean follow-up duration was 64.8 ± 31.5 months and 63.2 ± 28.1 months in the PS and varus–valgus constrained groups, respectively. The criterion of prosthesis choice was a subjective laxity assessed by the surgeon intraoperatively. A multivariate analysis was performed to evaluate the preoperative factors in the choice of the prosthesis.

Results

The grade of femoral bone defect was the only factor that affected the choice of prosthesis. Clinical results improved significantly in both groups after surgery. There were no significant differences in clinical results between the two groups. Complication rates were 9.5 % in the PS group and 10.1 % in the varus–valgus constrained group, and the Kaplan–Meier survivorship analysis revealed 8-year component survival rates of 83.1 and 93.0 % in the PS and varus–valgus constrained groups, respectively.

Conclusions

Femoral bone defect is an important factor to be considered in the choice of prosthesis for revision TKA. The varus–valgus constrained prosthesis showed an outcome similar to that of the PS prosthesis. For clinical relevance, varus–valgus constrained prosthesis is recommended in revision TKA when the PS prosthesis seems unsuitable for the management of instability.

Level of evidence

III.