Outcomes of cementless unicompartmental and total knee arthroplasty: A systematic review

Fixed-bearing medial unicompartmental knee arthroplasty restores pre-arthritic coronal alignment and achieves satisfactory functional outcomes: a retrospective study

PURPOSE

This study aimed to (1) analyze the Coronal Plane Alignment of the Knee (CPAK) classification in patients undergoing unicompartmental knee arthroplasty (UKA), (2) assess whether UKA can restore pre-arthritic coronal alignment by utilizing the arithmetic hip-knee-ankle angle (aHKA), and (3) evaluate the relationship between patient-reported outcome measures (PROMs) and postoperative alignment following UKA.

METHODS

We retrospectively analyzed 152 consecutive patients who underwent fixed-bearing medial UKA. A radiological analysis was conducted using an EOS imaging system. Postoperative alignment was classified as neutral (varus ≤ 3°), mild varus (3° < varus ≤ 7°), or marked varus (varus > 7°) based on the mechanical hip-knee-ankle angle (mHKA). The aHKA was calculated and the CPAK classification was used to categorize knee phenotypes. The PROMs were obtained both before and after the surgery.

RESULTS

A total of 152 knees from 113 patients were included with a mean two-year follow-up. The mean difference between the postoperative mHKA and the estimated aHKA was 0.80° (90% CI 0.35 to 1.24; P = 0.003). Postoperatively, 63 (41.45%) of the 152 knees were in neutral group, 54 (35.53%) mild varus, and 35 (23.03%) marked varus. The neutrally aligned cohort did not exhibit significantly higher scores in range of motion, VAS, HSS, WOMAC, or FJS-12 scores compared to the mild or marked varus cohort (P = 0.205, 0.118, 0.076, 0.140, and 0.788, respectively) during the short-term follow-up.

CONCLUSION

Non-robotically assisted, fixed-bearing medial UKA can restore pre-arthritic coronal alignment and achieve satisfactory PROMs. Fixed-bearing medial UKA aims to restore the pre-arthritic alignment rather than achieving neutral mechanical alignment.

Cemented Versus Cementless Unicompartmental Knee Arthroplasty

Unicompartmental knee arthroplasty (UKA) offers a more conservative treatment than total knee arthroplasty when osteoarthritis affects only one tibiofemoral knee compartment. Cemented UKA has become the gold standard due to its good functional outcomes and low revision rates. The most common reasons for revision with cemented UKA include aseptic loosing, unexplained pain, and radiolucent lines. Cementless UKA, which adds a porous coating of titanium and hydroxyapatite as well as an additional peg on the femoral component, has been shown to reduce the prevalence of radiolucencies compared to cemented UKAs. National registry data have demonstrated comparable functional outcomes and improved revision rates with cementless UKA. This review aims to summarize various advancements in unicompartmental prostheses, and to highlight how the conceptual advantages of the cementless model leads to superior implant survivorship and functional outcomes.

Cementless Total Knee Arthroplasty: Does Age Affect Survivorship and Outcomes?

BACKGROUND

Despite the growing popularity of cementless total knee arthroplasty (TKA) in younger patients, the outcomes are unclear in the elderly population. We aimed to compare the clinical outcomes and survivorship of cementless TKA between different age groups.

METHODS

Utilizing our prospectively collected institutional database, we retrospectively reviewed all patients undergoing primary cementless TKAs at a tertiary care institute. We identified 347 TKA, which were divided into 3 groups based on age at the time of surgery. Group A was ≤ 60 years, Group B was 60 to ≤ 70 years, and Group C was > 70 years. We compared clinical outcomes (Knee Society Clinical Rating System [KSCRS], Western Ontario and McMaster University Osteoarthritis Index [WOMAC], and Veterans Rand 12 Item Health Survey [VR-12]) and survivorship between the groups.

RESULTS

At final follow-up, range of motion, KSCRS, WOMAC, and VR-12 physical score were comparable (P > .05). The VR-12 Mental score was higher in Group B and Group C than in Group A (P = .003). Compared to preoperative scores, the change in KSCRS, WOMAC, and VR-12 physical and mental scores was comparable at the final follow-up (P > .05). No patient underwent revision for aseptic loosening.

CONCLUSIONS

There were no cases of revision surgery for aseptic loosening in our cohort of 347 cementless TKAs. Patients > 70 years of age undergoing cementless TKA can achieve clinical scores equivalent to those of younger patients at short term (2-year) follow-up. Longer-term survivorship is still required, but based on early data, cementless TKA can be a safe option for older patients.

Comparison of survival between cemented vs cementless unicompartimental knee arthroplasty: a case control study with propensity score matching

INTRODUCTION

The first results of cementless prosthesis were rather disappointing. However recent progress in methods of cementless fixation of prosthesis should lead to better results in terms of survival of these prostheses. The main objective is to compare the survival rate at last follow-up of UKA with cemented tibial or cementless.

HYPOTHESIS

We hypothesize that UKAs with uncemented tibial implants have better survival compared to UKAs with cemented tibial implants.

MATERIAL AND METHODS

This single center case-control study included 94 medial UKA with a cemented tibial component that were paired by propensity score matching to 94 medial UKA with a uncemented tibial component. The main evaluation criterion was the comparison of the survivorship of the UKA between a cemented tibial implant and those with a cementless tibial implant in terms of all-cause revision surgery at last follow-up. The secondary endpoints were the analysis of the causes of failure.

RESULTS

The mean final follow-up was 6.1years (2.3). The overall survival rate in our serie of medial UKA was 92.4% [88.7%-96.3%] at five years. The overall survival rate in cemented group was and 91.5% [86.0%-97.3%] at five years and at 93.2% [88.1%-98.7%] at five years, in the uncemented group. No differences significant were observed in the two groups (p.value = 0.6). Only the tibial preoperative deformity was a risk factor of failure (HR: 1.11 [1.02,1.20], value = 0.02).

DISCUSSION

The use of a cemented or a cementless tibial component in a medial UKA did not influence the survival rate.

LEVEL OF EVIDENCE

III; case control study.

[Successful medial unicompartmental knee arthroplasty-What are the most important surgical tricks?]

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is an established surgical treatment option for end-stage anteromedial osteoarthritis with excellent functional outcomes and implant survival. Routine preoperative varus and valgus stress views are crucial for the selection of patients for unicompartmental or total knee arthroplasty.

THERAPY

UKA is a soft-tissue based operation that aims to reconstruct the individual joint line and pre-arthritic alignment by restoring the physiological tension of the medial collateral and the cruciate ligaments.

RESULTS

Current data for medial UKA show excellent results for both mobile and fixed bearing implant designs with the correct indication and surgical technique. Cementless fixation offers potential advantages over cemented implants. Registry data demonstrate that institutions and surgeons specializing in partial knee replacement (> 30 cases/year per surgeon, > 100/year per institution) with a high percentage of UKA relative to the total number of knee implants (> 20%) have significantly lower revision rates.

Is Cementless Total Knee Arthroplasty Safe in Women Over 75 Y of Age?

BACKGROUND

Cementless total knee arthroplasty (TKA) is the subject of renewed interest. Previous concerns about survivorship have been addressed and there is an appeal in terms of biological fixation and surgical efficiency. However, even surgeon advocates have concerns about the risk of marked subsidence when using this technology in older patients at risk for osteoporosis.

METHODS

This was a retrospective analysis of 1,000 consecutive fully cementless mobile bearing TKAs performed at a single institution on women over 75 years of age who had postoperative and 1-year x-rays. The primary outcome was the incidence of subsidence.

RESULTS

There were three asymptomatic cases with definite subsidence and change in alignment. In a fourth symptomatic case, the femoral component subsided into varus and the tibia into valgus, thus maintaining alignment which facilitated nonoperative treatment in a 92-year-old. Overall, at 1 year, there were two- liner revisions for infection without recurrence. Five patients had further surgery, of which three were washouts and two were for periprosthetic fractures sustained postoperatively within 1 year. Seven patients had further anesthesia, of which five were manipulations and two were nonrecurrent closed reductions for spinouts.

CONCLUSION

Cementless TKA did not have a high risk of subsidence in this at-risk population. In the hands of experienced surgeons, these procedures can be used safely irrespective of bone quality.

Survivorship, clinical outcomes and indications for revision in uncemented unicompartmental knee arthroplasty: systematic review

Modern uncemented unicompartmental knee arthroplasty (UKA) relies on the mechanics of the implant design and a biological bond at the bone-implant interface to create a secure fixation of its components. The aim of this systematic review was to determine implant survivorship, clinical outcomes and indications for revision in uncemented UKAs. A search strategy was employed using keywords related to UKAs and uncemented fixation to identify suitable studies. Both prospective and retrospective studies with a minimum of two year mean follow-up were included. Data was gathered on study design, implant type, patient demographics, survivorship, clinical outcome scores and the indications for revision. Methodological quality was assessed using a ten-point risk of bias scoring tool. Eighteen studies were included in the final review. The mean follow-up of studies ranged between 2-11 years. The primary outcome of survival demonstrated 5 year survivorship ranged between 91.7-100.0% and 10-year survivorship between 91.0-97.5%. Clinical and functional outcome scores were found to be excellent in the majority of studies with the remaining reporting good results. Revisions represented 2.7% of the total operations performed. There were 145 revisions with an overall revision rate of 0.8 per 100 observed component years. Osteoarthritis disease progression (30.2%) and bearing dislocations (23.8%) were the most common causes of implant failure. This review finds uncemented UKAs demonstrate comparable survivorship, clinical outcomes and safety profile to cemented UKAs to consider this fixation a suitable alternative in clinical use.

No component loosening of a cementless deep dish rotating platform knee at a 5-year follow-up

PURPOSE

Cemented fixation remains the gold standard in total knee arthroplasty. With an increasing number of younger patients undergoing total knee arthroplasty and a growing patient population demanding higher physical activity, a rising interest in discussion of cementless fixation is notable. The current scientific literature does not give a clear recommendation for or against uncemented total knee arthroplasty. The purpose of this study was the investigation of the 5-year clinical and radiographic outcomes of a cementless deep-dish rotating platform implant.

METHODS

A total of 91 primary cementless total knee arthroplasties were included in this single-centre prospective observational study. The primary outcome was revision rate due to aseptic component loosening. Further outcome measures were assessment of the of the radiographic outcome as well as the clinical outcome based on Range of Motion and scores such as American Knee Society Score, Oxford Knee Score, Knee Injury and Osteoarthritis Outcome Score and European Quality of Life 5 Dimension 3 Level at a follow-up of 5 years.

RESULTS

Mean age of the study population was 67.3 ± 6.6 years with 49.5% of the participants being female. Aseptic component loosening occurred in none of the patients. Implant survival with revision for any reason as endpoint was 97.8% (95% CI 100-96%) and 95.6% (95% CI 100-94%) with reoperation of any cause as endpoint. Radiolucent lines were detected in a total of eight cases (8.8%) and disappeared within the first year after surgery in five cases. Total Range of Motion improved significantly from 106° ± 15° preoperatively to 118° ± 10° at final FU (p < 0.001). All investigated scores improved significantly after total knee arthroplasty.

CONCLUSION

The results of this study reveal excellent mid-term performance of a cementless deep dish rotating platform total knee implant, with no component loosening, very low overall revision rate, only temporarily present radiolucent lines in a minority of patients and excellent clinical results. Therefore, cementless total knee arthroplasty is an appropriate treatment option for patients with severe osteoarthritis of the knee.

LEVEL OF EVIDENCE

Level II (prospective cohort study).

Impact of keel saw blade design and thickness on the incidence of tibial plateau fracture and tibial implant-loosening in cementless medial UKR

BACKGROUND

Tibial plateau fractures and tibial implant- loosening are severe complications in cementless unicompartmental knee replacement (UKR). The tibial keel preparation is particularly demanding and different saw blades can be used. It was hypothesized that different blade designs and thickness have an influence on the frequency of tibial plateau fractures and implant-loosening in cementless medial UKR.

METHODS

1258 patients with cementless medial UKR were included in this retrospective study between 2013 and 2020. The tibial keel cut was performed either with a double keel saw blade (DKS; 2.8 mm) and added hand guided pick or a mono reciprocating saw blade (RKB) of different thickness (2.5 mm; 2.65 mm; 2.75 mm). Tibial plateau fracture and loosening were demonstrated by standard two-plane radiographs. Tibial implant-loosening was defined as complete radiolucency and implant migration. Fracture and loosening were combined with pain and loss of function.

RESULTS

In 126 patients (10%) the tibial keel was prepared with DKS, in 407 patients (32.4%) with RKB 2.5 mm, in 330 patients (26.2%) with RKB 2.65 mm and in 395 patients (31.4%) with 2.75 mm. In 4 patients (3.17%) with DKS tibial plateau fracture occurred, in 4 patients (0.99%) with 2.5 mm RKB, in 3 patients (0.92%) with 2.65 mm RKB and in 1 patient (0.25%) with 2.75 mm RKB. Significantly fewer fractures occurred with a RKB design (p = 0.007). A negative correlation between fracture incidence and RKB saw blade thickness was found (Spearman-r = - 0.93). No difference for tibial implant-loosening was shown (p = 0.51).

CONCLUSION

Different blade designs and thickness have a significant influence on the incidence of tibial plateau fractures and aseptic tibial implant-loosening. The incidence of tibial plateau fractures in cementless medial UKR can be reduced by changing the design and thickness of the tibial keel saw blade. Greater thickness of RKB leads to significantly fewer tibial plateau fractures while the incidence of implant-loosening is not increasing.

TRIAL REGISTRATION

This study was retrospectively registered and ethical approval was waived by the local ethical committee (No. 2020-1174).

Analysis of different geometrical features to achieve close-to-bone stiffness material properties in medical device: A feasibility numerical study

BACKGROUND AND OBJECTIVE

In orthopedic medical devices, elasto-plastic behavior differences between bone and metallic materials could lead to mechanical issues at the bone-implant interface, as stress shielding. Those issue are mainly related to knee and hip arthroplasty, and they could be responsible for implant failure. To reduce mismatching-related adverse events between bone and prosthesis mechanical properties, modifying the implant's internal geometry varying the bulk stiffness and density could be the right approach. Therefore, this feasibility study aims to assess which in-body gap geometry improves, by reducing, the bulk stiffness.

METHODS

Using five finite element models, a uniaxial compression test in five cubes with a 20 mm thickness was simulated and analyzed. The displacements, strain and Young Modulus were calculated in four cubes, each containing internal prismatic gaps with different transversal sections (squared, hexagonal, octagonal, and circular). Those were compared with a fifth full-volume cube used as control.

RESULTS

The most significant difference have been achieved in displacement values, in cubes containing internal gaps with hexagonal and circular transversal sections (82 µm and 82.5 µm, respectively), when compared to the full-volume cube (69.3 µm).

CONCLUSIONS

This study suggests that hexagonal and circular shape of the gaps allows obtaining the lower rigidity in a size range of 4 mm, offering a starting approach to achieve a "close-to-bone" material, with a potential use in prosthetic devices with limited thickness.

Ultra-Pulsed CO2 Laser Osteotomy: A New Method for the Bone Preparation of Total Knee Arthroplasty

Cementless total knee arthroplasty (TKA) can achieve long-term biological fixation, but its application is limited by the risk of early aseptic loosening. One of the important reasons for early aseptic loosening is that mechanical osteotomy tools cannot achieve ideal bone preparation because of poor accuracy and serious bone tissue damage produced by them. Therefore, we designed an ultra-pulsed CO₂ laser osteotomy system to solve these problems. To reveal the safety at the tissue and cell levels of the ultra-pulsed CO₂ laser osteotomy system, a series of experiments on distal femur osteotomy in animals were performed. Then, the bone surface characteristics were analyzed through scanning electron microscopy, and the bone thermal and mechanical damage was evaluated via histological analysis. Finally, mesenchymal stem cells (MSCs) were inoculated on the bone surfaces prepared by the two osteotomy tools, and the effect of cell adhesion was analyzed through a confocal laser scanning microscope (CLSM). We successfully achieved TKA bone preparation of animal knees with the ultra-pulsed CO₂ laser osteotomy system. Moreover, the biological evaluation results indicated that compared with the traditional mechanical saw, the laser can preserve the natural bone structure and cause no thermal damage to the bone. In addition, CLSM examination results showed that the laser-cut bone surface was more conducive to cell adhesion and infiltration than the bone surface cut by a mechanical saw. Overall, these results indicate that ultra-pulsed CO₂ laser can achieve non-invasive bone cutting, which can be a new option for TKA bone preparation and has the potential to lead in the future.

Highlighting the advantages and benefits of cementless total knee arthroplasty (Review)

In the field of orthopedic surgery, cemented total knee arthroplasty (TKA) is considered to be one of the gold standards. However, there are categories of patients (i.e., obese and morbidly obese patients, younger than 65 years old) among whom cemented TKA has however a high failure rate. Moreover, the frequency of using uncemented TKA is increasing due to the potential benefits of long-term biological fixation, being an innovative field that addresses a new generation orthopedic surgical treatment which is more suitable for young patients who have good bone quality (good to very good, in terms of density). The survival rates and functional results of the latest generation of cementless TKAs may be similar to functional results and survival rates of cemented prosthesis. In conclusion, this review-type article can be considered a powerful database, extremely informative, dense, and focused on the topic mentioned above, in the interest of all medical professionals and all interested individuals.

Comparable mid-term revision rates of primary cemented and cementless total knee arthroplasties in 201,211 cases in the Dutch Arthroplasty Register (2007-2017)

PURPOSE

Long-term failure of total knee arthroplasty (TKA) is mostly due to loosening of the prosthesis. In this study, the short- and mid-term revision rates of cemented vs cementless TKAs were investigated. Comparable short- and mid-term survival rates of both fixation methods were expected.

METHODS

Data on all cemented and cementless TKAs performed between 2007 and 2017 were retrieved from the Dutch Arthroplasty Register. The cumulative crude incidence of revision of cemented and cementless TKA was calculated. Death was considered a competing risk. Revision rates were compared using multivariable Cox proportional hazard regression analysis. The associations between fixation method and type of revision or reason for revision were tested using logistic regression analyses.

RESULTS

In total, 190,651 (94.8%) cemented and 10,560 (5.3%) cementless TKAs were evaluated. Both groups had comparable case characteristics. Cemented TKAs were inserted more often in cases with previous knee surgery compared to cementless TKAs (32% vs 27%). The cumulative incidence of revision after 9 years was 5.5% (CI 5.3-5.6%) for cemented and 5.8% (CI 5.2-6.4%) for cementless TKAs (p = 0.2). Cementless TKAs were more often revised due to loosening of the tibial (27% vs 18%; p < 0.001) or the femoral component (7% vs 5%; p = 0.005) than cemented TKAs. Cemented TKAs were more often revised due to infection (17% vs 9%; p = 0.004) than cementless TKAs.

CONCLUSION

In conclusion, cemented and cementless TKAs have comparable short- and mid-term revision rates based on a nationwide register study.

LEVEL OF EVIDENCE

III.

The Association Between Cement Viscosity and Revision Risk After Primary Total Knee Arthroplasty

BACKGROUND

Recent case series have reported early failure with the use of high-viscosity cement (HVC) in total knee arthroplasty (TKA). We evaluated revision risk after TKA with HVC compared with medium-viscosity cement (MVC) in a large cohort.

METHODS

We conducted a cohort study using data from Kaiser Permanente's Total Joint Replacement Registry. Patients who underwent fully cemented primary TKA for osteoarthritis were identified (2001-2018). Only posterior-stabilized, fixed-mobility designs of the 3 highest-volume implant systems (DePuy PFC, Zimmer NexGen, and Zimmer Persona) were included to mitigate confounding from implant characteristics. Palacos (Zimmer/Heraeus) and Simplex (Stryker) cements comprised the HVC and MVC exposure groups, respectively. Propensity score-weighted Cox proportional hazards regression was used to evaluate risk for any revision during follow-up and risk for revision from aseptic loosening specifically.

RESULTS

The final cohort comprised 76,052 TKAs, 41.1% using MVC. The crude 14-year cumulative revision probability was 4.55% and 5.12% for TKA with MVC and HVC, respectively. In propensity score-weighted Cox models, MVC compared with HVC had a lower risk of any revision (hazard ratio = 0.82, 95% confidence interval = 0.70-0.95) while no difference was observed for revision from aseptic loosening (hazard ratio = 0.80, 95% confidence interval = 0.56-1.13).

CONCLUSION

While we observed a lower risk for any revision with the use of Simplex MVC compared with Palacos HVC, we did not observe a difference in revision for aseptic loosening specifically. Given the widespread use of HVC, additional research to investigate other HVC and potential mechanisms for failure outside of loosening is warranted.

LEVEL OF EVIDENCE

Level III.

Trends in Operative Time and Short-Term Outcomes After Conventional and Navigated Total Knee Arthroplasty

BACKGROUND

Adoption of navigated total knee arthroplasty (Nav-TKA) is increasing. However, it has been suggested that a perceived decrease in surgical efficiency and a lack of proven superior functional outcomes associated with Nav-TKA have hindered its widespread adoption.

METHODS

The American College of Surgeons National Surgical Quality Improvement Program was queried to identify patients who had undergone TKA with or without navigation between 2012 and 2018. Patients were further subclassified based on the type of navigation used, image-guided or imageless. Multivariate logistic regression was used to compare operative time and 30-day complication rates between conventional TKA (Conv-TKA) and Nav-TKA with and without image guidance.

RESULTS

A total of 316,210 Conv-TKAs and 8554 Nav-TKAs (8270 imageless, 284 image-guided) were identified. Across the study period, the use of Nav-TKA was associated with a 1.5-minute increase in operative time. However, the overall time burden decreased over the study period, and by 2018, the mean operative time for Nav-TKA was 2.4 minutes less than that of Conv-TKA. Compared with Conv-TKA, Nav-TKA was associated with decreased rates of postoperative transfusion and surgical site complications but a similar incidence of systemic thromboembolism.

CONCLUSIONS

This is the first large-scale database study to examine the differences in operative time between Conv-TKA and Nav-TKA. The time burden associated with Nav-TKA decreased over the study period and even reversed by 2018. Nav-TKA was associated with lower rates of postoperative transfusion and surgical site complications. Further studies are needed to evaluate the long-term and functional outcomes between conventional and navigated knee arthroplasty techniques.

Trends and developments in hip and knee arthroplasty technology

The developments in hip and knee arthroplasty over recent years have aimed to improve outcomes, reduce complications and improve implant survival. This review describes some of the most interesting trends and developments in this important and fast-moving field. Notable developments have included ceramic hip resurfacing, mini hip stems, cementless knee replacement and the wider adoption of the dual mobility articulation for hip arthroplasty. Advances in additive manufacturing and the surface modification of joint replacements offer increasing options for more challenging arthroplasty cases. Robotic assisted surgery is one of the most interesting developments in hip and knee surgery. The recent growth in the use of this technology is providing data that will help determine whether this approach should become the standard of care for hip and knee arthroplasty in the future.

Cementless knee arthroplasty: a review of recent performance

Cementless knee arthroplasty has seen a recent resurgence in popularity due to conceptual advantages, including improved osseointegration providing biological fixation, increased surgical efficiency, and reduced systemic complications associated with cement impaction and wear from cement debris. Increasingly younger and higher demand patients are requiring knee arthroplasty, and as such, there is optimism cementless fixation may improve implant survivorship and functional outcomes.

Compared to cemented implants, the National Joint Registry (NJR) currently reports higher revision rates in cementless total knee arthroplasty (TKA), but lower in unicompartmental knee arthroplasty (UKA). However, recent studies are beginning to show excellent outcomes with cementless implants, particularly with UKA which has shown superior performance to cemented varieties. Cementless TKA has yet to show long-term benefit, and currently performs equivalently to cemented in short- to medium-term cohort studies. However, with novel concepts including 3D-printed coatings, robotic-assisted surgery, radiostereometric analysis, and kinematic or functional knee alignment principles, it is hoped they may help improve the outcomes of cementless TKA in the long-term. In addition, though cementless implant costs remain higher due to novel implant coatings, it is speculated cost-effectiveness can be achieved through greater surgical efficiency and potential reduction in revision costs. There is paucity of level one data on long-term outcomes between fixation methods and the cost-effectiveness of modern cementless knee arthroplasty.

This review explores recent literature on cementless knee arthroplasty, with regards to clinical outcomes, implant survivorship, complications, and cost-effectiveness; providing a concise update to assist clinicians on implant choice.

Cite this article: Bone Jt Open 2021;2(1):48–57.

Excellent survival and outcomes with fixed-bearing medial UKA in young patients (≤ 60 years) at minimum 10-year follow-up

PURPOSE

To evaluate whether long-term (10-year minimum) patient outcomes and survival of fixed-bearing medial unicompartmental knee arthroplasty (UKA) in patients aged  ≤ 60 years were favorable despite non-conventional age criteria.

METHODS

The authors reviewed the records of 91 consecutive medial UKAs performed in patients aged ≤ 60 by a single surgeon. All patients received the same fixed-bearing M/G Unicompartmental Knee System. Patients records were updated, noting complications or revisions, and Oxford Knee Scores and overall satisfaction collected. If deceased, the general practitioner or next of kin provided data.

RESULTS

Of the initial 91 knees, 10 were revised, 6 were deceased, and 1 was lost to follow-up. The final cohort of 74 knees was aged 54.3 ± 4.3 years (range 41.8-60.6) at index surgery. Using revision of any component as endpoint, the present series had a KM survival of 92.9% (CI 84.8-96.7%) at 10 years, and 87.8% (CI 78.4-93.2%) at 15 years, and a single non-fatal DVT was reported. At final follow-up of 15 ± 1.3 years (range 11-18), OKS (available for all 74 knees) was 38.4 ± 8.4 (range 18-48). Overall patients were pleased or very pleased with 72 of the knees (97%).

CONCLUSION

Fixed-bearing medial UKA yields favorable results in the treatment of single compartment osteoarthritis of the knee in patients ≤ 60 years. The present study demonstrates low complication rates, good-to-excellent long-term patient outcomes, and satisfactory implant survival for this age group considering the advantages of UKA.

LEVEL OF EVIDENCE

Level IV, retrospective cohort study.

Short-term results of triathlon cementless versus cemented primary total knee arthroplasty

BACKGROUND

Recent studies have demonstrated that aseptic loosening remains a leading cause of failure after total knee arthroplasty (TKA). Cementless fixation is a possible strategy for countering this problem. This study compared short-term survivorship and functional results of patients undergoing primary TKA with cementless versus cemented implants.

METHODS

A multi-center database was utilized to identify 3849 patients undergoing primary TKA between 2012 and 2017 with a minimum two-year follow-up. Patients were divided into cementless (699), and cemented TKA (3150). The outcome of TKA including revision for aseptic or septic reasons, and other outcome variables were compared. Six hundred five patients from the cementless group (case) were matched with 605 patients from the cemented group (controls). Both groups were compared for outcomes and related variables.

RESULTS

Both matched groups were similar in age, race, gender, height, weight, BMI, laterality, femoral component type, follow-up duration, preoperative and postoperative physical and mental health, and functional activities (all p-values>0.05). Although the cementless TKA group had more components in varus alignment (p = 0.015) and were taller (p < 0.001), the aseptic revision rate and time to failure were similar in both groups (p-values = 0.256 and 0.0890 respectively). The rate of revision for infection was also the same in both groups (p = 0.452).

CONCLUSION

Cementless TKA demonstrated an equivalent rate of aseptic and septic failure when compared to cemented TKA in the short-term. Time to aseptic failure was also similar in both groups.

Cemented vs Uncemented Femoral Components: A Randomized, Controlled Trial at 10 Years Minimum Follow-Up

BACKGROUND

The type of total knee arthroplasty (TKA) fixation (cemented or uncemented) is still subject to debate. The aim of this study is to assess the survival rate, clinical outcomes, and radiological results of TKA according to the fixation type.

METHODS

A total of 130 patients were randomly assigned to either the cement group (cemented femoral and tibial implants) or the hybrid group (cemented tibial implant, uncemented femoral implant). The inclusion criteria were patients between 50 and 90 years old who underwent primary TKA for osteoarthritis between 2004 and 2005 without a history of open knee surgery. Revisions and complications were reported, as well as clinical scores and radiological signs of loosening.

RESULTS

One hundred eighteen patients had complete data at 10 years of minimum follow-up (59 in each group). The mean age was 72 years old. The mean follow-up was 13 years. The survival rate was 98% at 13 years in both groups (1 aseptic loosening at 2 years in the cement group, 1 septic loosening in the hybrid group). The complication rate in the cement group was 8.5% (n = 5) vs 12.1% (n = 7) in the hybrid group (P = .8). The clinical results were not significantly different. In the cement group, 25% of patients (n = 15) had radiolucent lines at 10 years. In the hybrid group, 33% of patients had bone transparencies, not evolving or symptomatic.

CONCLUSION

At a minimum follow-up of 10 years, there were no significant differences between cemented TKA and hybrid TKA for the survivorship, the complication rate, the clinical scores, or the radiological signs of loosening.

LEVEL OF EVIDENCE

I.

Cementless Oxford Medial Unicompartmental Knee Replacement-Clinical and Radiological Results of 228 Knees with a Minimum 2-Year Follow-Up

(1) Background: Studies show several advantages of unicompartmental knee replacement (UKR) over total knee replacements (TKR), whereas registry based revision rates of UKR are significantly higher than for TKA. Registry data report lower revision rates for cementless UKR compared to cemented UKR. The aim of this study was to assess clinical and radiological results of cementless Oxford UKR (OUKR) in an independent cohort. (2) Methods: This retrospective cohort study examines a consecutive series of 228 cementless OUKR. Clinical outcome was measured using functional scores (Oxford Knee Score (OKS), American Knee Society Score (AKSS), Hannover Functional Ability Questionnaire for Osteoarthritis (FFbH-OA), range of motion (ROM)), pain and satisfaction. Radiographs were analyzed regarding the incidence of radiolucent lines (RL), implant positioning, and their possible impact on clinical outcome. (3) Results: At a mean follow-up of 37.1 months, the two and three year revision free survival-rates were 97.5% and 96.9%. Reasons for revision surgery were progression of osteoarthritis, inlay dislocation and pain. All clinical outcome scores showed a significant improvement from pre- to postoperative. The incidence of RL around the implant was highest within the first year postoperatively (36%), and decreased (5%) within the second year. Their presence was not correlated with inferior clinical outcome. Implant positioning showed no influence on clinical outcome. (4) Conclusion: Cementless OUKR showed excellent clinical outcome and survival rates, with reliable osteointegration. Neither the incidence of radiolucent lines nor implant positioning were associated with inferior clinical outcome.

Effect of bone density and cement morphology on biomechanical stability of tibial unicompartmental knee arthroplasty

BACKGROUND

Unicompartmental knee arthroplasty (UKA) offers good long-term survivorship and superior kinematics and function compared with total knee arthroplasty (TKA). However, revision rates are higher with aseptic loosening representing a major cause. Biomechanical stability depends on cement penetration. The goal of this study was to analyze the influence of cement morphology and bone density on primary stability of tibial UKA under physiological loading conditions in human tibiae.

METHODS

Thirty-six tibial trays were implanted in fresh-frozen human cadaver knees and tested for primary stability using dynamic compression-shear testing. Prior to implantation, bone density had been quantified for all 18 tibiae. Postoperatively, cement penetration has been assessed on frontal cuts based on eight predefined parameters. The influence of bone density and cement morphology on biomechanical stability was determined using correlation and linear regression analysis.

RESULTS

Mean failure load was 2691 ± 832.9 N, mean total cement thickness was 2.04 ± 0.37 mm, mean cement penetration was 1.54 ± 0.33 mm and mean trabecular bone mineral density (BMD) was 107.1 ± 29.3 mg/ml. There was no significant correlation between failure load and cement morphology (P > .05). Failure load was significantly positive correlated with trabecular BMD (r = 0.843; P < .0001) and cortical BMD (r = 0.432; P = .0136).

CONCLUSIONS

Simulating physiological loading conditions, the failure load of tibial UKA is linearly dependent on the trabecular BMD. The observed parameters of cementation morphology seem capable of preventing failure at the bone-cement interface before inherent bone stability is reached. Further research is required to assess the usefulness of a preoperative assessment of bone quality for patient selection in UKA.

Observational Study of Total Knee Arthroplasty in Aseptic Revision Surgery: Clinical Results

OBJECTIVE

To review the long-term clinical results after revision surgery and the relationship between the different clinical variables involved with a failed total knee arthroplasty (TKA) and its evolution to provide a better understanding of the current treatment methods.

METHODS

The present study involved 89 subjects with a failed knee arthroplasty that ended up requiring revision surgery and component replacement between 2011 and 2015. The study included patients with pain remaining after TKA and indication from the knee unit surgeon to review the implant, without presenting with thromboembolic or neurological changes that could bias the results. The demographic data, surgical information, type of implant, and causes of failure were analyzed. The patients subjected to replacement surgery were specifically asked to fill out clinical and satisfaction questionnaires (Lysholm and KOOS). The mean follow-up was 5.6 years (range, 3-11 years) and the analysis was divided into early revision (<5 years) and late revision (>5 years). The R statistical package version 3.2.5 for Windows was used, with significance less than 0.05 Cohort observational study.

RESULTS

The results indicated that implant revisions accounted for 5.57% of total primary implants, with a mean survival of 6 years for primary prosthesis failure. The mean revision surgery result on the Lysholm knee scoring scale was 68.73 out of 100 points. A better score was obtained for revisions undertaken on TKA with over 5 years' survival and there were no significant differences in terms of the type of implant used. The causes of TKA failure were aseptic loosening (77.38%), instability (9.52%), and painful prosthesis (13.10%). The results were statistically significant when isolated revisions were performed on one component. Rating worse on most of the questionnaire subscales.

CONCLUSION

The clinical results were better in primary implant replacements with at least 5 years' survival. The replacement of only one of the components (tibial or femoral) provided worse clinical results than total replacement.

Early Results of a Modern Uncemented Total Knee Arthroplasty System

Historically, cementless total knees were associated with early failure, which made cemented total knee arthroplasty the gold standard. Manufacturers have introduced newer uncemented technologies that provide good initial stability and use highly porous substrates for bony in-growth. The authors hypothesized that the implants would have equivalent 90-day clinical and economic outcomes. Prospectively collected data on 252 uncemented knees in the Michigan Arthroplasty Registry Collaborative Quality Initiative database were reviewed. Ninety-day outcomes, demographics, length of stay, complications, emergency department visits, readmissions, and financial data were compared with those of an age-matched group of cemented knees. Uncemented knees had shorter length of stay (1.58 vs 1.87 days; P<.01), were more frequently discharged home (90.48% vs 68.75%; P<.0001), and used less home care (6.35% vs 19.14%; P<.0001) or extended care facilities (2.78% vs 11.72%; P=.0001). More uncemented knees had "no complications." Moreover, there were no re-operations in uncemented knees, compared with 19 reoperations in cemented knees. Uncemented knees were better than age-matched counterparts for Knee injury and Osteoarthritis Outcome Score (63.69 vs 47.10, n=85 and n=43, P<.0001) and Patient-Reported Outcomes Measurement Information System (PROMIS) T-Physical and T-Mental scores (44.12 vs 39.45, P<.0001; 51.84 vs 47.82, P=.0018). Cemented cases were more expensive overall, and surgical ($6806.43 vs $5710.78; P<.01) and total hospital ($8347.65 vs $7016.11; P<.01) costs were higher. The 90-day readmission and hospital outpatient costs were not significantly different between designs. Uncemented total knee arthroplasty, when using modern technologies, is successful and economically viable for an at-risk bundle. The results of this study should alleviate fears of increased cost, early failure, complications, or poor outcomes with the use of a modern uncemented total knee arthroplasty. [Orthopedics. 2019; 42(6):355-360.].

Despite Improved Survivorship of Uncemented Fixation in Total Knee Arthroplasty for Osteoarthritis, Cemented Fixation Remains the Gold Standard: An Analysis of a National Joint Registry

BACKGROUND

Total knee arthroplasty (TKA) numbers are increasing worldwide. While cement fixation for both femoral and tibial components is commonly used, alternatives include hybrid and uncemented TKAs. This study aimed to evaluate survivorship, revision rates, and patient-reported outcomes for cemented, hybrid, and uncemented TKAs using New Zealand Joint Registry (NZJR) data.

METHODS

NZJR data relating to all TKAs performed during the 19 years up to the end of December 2017 were analyzed. Outcomes were assessed using prosthesis survivorship data (including reasons for revision) and Oxford scores at 6 months, 5 years, and 10 years postoperatively.

RESULTS

A total 96,519 primary TKAs were performed during the period examined. Most (91.5%) were fully cemented with 4.8% hybrid and 3.7% uncemented. Mean Oxford scores at 6 months were highest in cemented and lowest in uncemented TKAs (P < .001). However, this was not clinically significant. There was no difference at 5 or 10 years. Ten-year survival rates were 97%, 94.5%, and 95.8% for cemented, uncemented, and hybrid TKAs, respectively. Revision rates were 0.47, 0.74, and 0.52 per 100 component years for cemented, uncemented, and hybrid prostheses, respectively. The revision rate for uncemented prostheses compared with cemented was higher (P < .001). When stratified by age group, there were differences in survival rates between cemented and uncemented groups (P = .001) and hybrid and uncemented groups (P = .038) in patients aged <55 years; between cemented and uncemented groups in those aged 55-64 years (P = .031); and between cemented and hybrid groups in those aged >75 years (P = .004).

CONCLUSION

Uncemented TKAs had similar patient-reported outcomes but higher revision rates and worse survivorship compared with hybrid or fully cemented TKAs.

An increased body mass index was not associated with higher rates of 30-day postoperative complications after unicompartmental knee arthroplasty

BACKGROUND

The association of postoperative complications and obesity after total knee arthroplasty (TKA) has been well described. However, the effect of an increased body-mass index (BMI) on postoperative complications after unicompartmental knee arthroplasty (UKA) is controversial. Therefore, our aim was to assess the influence of BMI on 30-day postoperative complications after UKA when analyzed as both a categorical and continuous variable.

METHODS

The American College of Surgeons National Quality Improvement Program (NSQIP) database was used to identify a total of 8029 patients who underwent UKA from January 1, 2008, to December 31, 2016. The database was queried for over 30 unique complications occurring within 30 days. The impact of BMI on short-term outcomes was assessed as a categorical variable using univariate and multivariate regression. Additionally, BMI was assessed as a continuous variable using spline regressions.

RESULTS

Univariate regression analysis revealed that compared to normal weight patients, overweight patients had a lower risk of major complication (odds ratio [OR], 0.506; 95% confidence interval [CI], 0.279-0.918; p = 0.025), and any complication ([OR] 0.632; 95% CI, 0.423-0.944; p = 0.025) Multivariate regression analysis found no statistically significant relationship between categorical BMI and complications or outcomes, except for morbidly obese patients who had a greater risk of superficial SSI (p = 0.026). Spline regression found no statistically significant non-linear relationships between BMI and any complication (p = 0.4687), major complications (p = 0.1567), or minor complications (p = 0.4071).

CONCLUSION

Overweight and obese individuals who undergo UKA may not have an increased risk of 30-day postoperative complications compared to normal weight individuals.

Patient relevant outcomes of unicompartmental versus total knee replacement: systematic review and meta-analysis

OBJECTIVE

To present a clear and comprehensive summary of the published data on unicompartmental knee replacement (UKA) or total knee replacement (TKA), comparing domains of outcome that have been shown to be important to patients and clinicians to allow informed decision making.

DESIGN

Systematic review using data from randomised controlled trials, nationwide databases or joint registries, and large cohort studies.

DATA SOURCES

Medline, Embase, Cochrane Controlled Register of Trials (CENTRAL), and Clinical Trials.gov, searched between 1 January 1997 and 31 December 2018.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies published in the past 20 years, comparing outcomes of primary UKA with TKA in adult patients. Studies were excluded if they involved fewer than 50 participants, or if translation into English was not available.

RESULTS

60 eligible studies were separated into three methodological groups: seven publications from six randomised controlled trials, 17 national joint registries and national database studies, and 36 cohort studies. Results for each domain of outcome varied depending on the level of data, and findings were not always significant. Analysis of the three groups of studies showed significantly shorter hospital stays after UKA than after TKA (-1.20 days (95% confidence interval -1.67 to -0.73), -1.43 (-1.53 to -1.33), and -1.73 (-2.30 to -1.16), respectively). There was no significant difference in pain, based on patient reported outcome measures (PROMs), but significantly better functional PROM scores for UKA than for TKA in both non-trial groups (mean difference -0.58 (-0.88 to -0.27) and -0.32 (-0.48 to -0.15), respectively). Regarding major complications, trials and cohort studies had non-significant results, but mortality after TKA was significantly higher in registry and large database studies (risk ratio 0.27 (0.16 to 0.45)), as were venous thromboembolic events (0.39 (0.27 to 0.57)) and major cardiac events (0.22 (0.06 to 0.86)). Early reoperation for any reason was higher after TKA than after UKA, but revision rates at five years remained higher for UKA in all three study groups (risk ratio 5.95 (1.29 to 27.59), 2.50 (1.77 to 3.54), and 3.13 (1.89 to 5.17), respectively).

CONCLUSIONS

TKA and UKA are both viable options for the treatment of isolated unicompartmental osteoarthritis. By directly comparing the two treatments, this study demonstrates better results for UKA in several outcome domains. However, the risk of revision surgery was lower for TKA. This information should be available to patients as part of the shared decision making process in choosing treatment options.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO number CRD42018089972.

How long does a knee replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up

BACKGROUND

Knee replacements are the mainstay of treatment for end-stage osteoarthritis and are effective. Given time, all knee replacements will fail and knowing when this failure might happen is important. We aimed to establish how long a knee replacement lasts.

METHODS

In this systematic review and meta-analysis, we searched MEDLINE and Embase for case series and cohort studies published from database inception until July 21, 2018. Articles reporting 15 year or greater survival of primary total knee replacement (TKR), unicondylar knee replacement (UKR), and patellofemoral replacements in patients with osteoarthritis were included. Articles that reviewed specifically complex primary surgeries or revisions were excluded. Survival and implant data were extracted, with all-cause survival of the knee replacement construct being the primary outcome. We also reviewed national joint replacement registry reports and extracted the data to be analysed separately. In the meta-analysis, we weighted each series and calculated a pooled survival estimate for each data source at 15 years, 20 years, and 25 years, using a fixed-effects model. This study is registered with PROSPERO, number CRD42018105188.

FINDINGS

From 4363 references found by our initial search, we identified 33 case series in 30 eligible articles, which reported all-cause survival for 6490 TKRs (26 case series) and 742 UKRs (seven case series). No case series reporting on patellofemoral replacements met our inclusion criteria, and no case series reported 25 year survival for TKR. The estimated 25 year survival for UKR (based on one case series) was 72·0% (95% CI 58·0-95·0). Registries contributed 299 291 TKRs (47 series) and 7714 UKRs (five series). The pooled registry 25 year survival of TKRs (14 registries) was 82·3% (95% CI 81·3-83·2) and of UKRs (four registries) was 69·8% (67·6-72·1).

INTERPRETATION

Our pooled registry data, which we believe to be more accurate than the case series data, shows that approximately 82% of TKRs last 25 years and 70% of UKRs last 25 years. These findings will be of use to patients and health-care providers; further information is required to predict exactly how long specific knee replacements will last.

FUNDING

The National Joint Registry for England, Wales, Northern Ireland, and Isle of Man and the Royal College of Surgeons of England.

Component Placement Accuracy in Unicompartmental Knee Arthroplasty Is Improved with Robotic-Assisted Surgery: Will It Have an Effect on Outcomes?

Bell et al.'s "Improved Accuracy of Component Positioning with Robotic-Assisted Unicompartmental Knee Arthroplasty: Data from a Prospective, Randomized Controlled Study" compared the accuracy of a robotic-assisted unicompartmental knee arthroplasty (UKA) using the MAKO Robotic Interactive Orthopedic Arm (RIO) system to a conventional UKA using standardized instrumentation. This review examines the authors' findings and their relevance to clinical practice. Bell et al. conclude that the MAKO RIO system leads to more accurate implantation of both the tibial and femoral components in UKA in the sagittal, coronal, and axial planes. This well-designed, level I study suggests what many arthroplasty surgeons assume about robotic assistance, which admittedly is of unknown clinical significance at this time. Evaluating this article in the context of the current literature provides valuable insight into areas in need of future investigation. The effect of implant positioning on long-term clinical outcomes and implant survivorship remains unclear. Long-term follow-up studies are needed to determine the role of robotic-assisted arthroplasty in the future.

SPECT/CT in the Postoperative Painful Knee

This review summarizes the role of SPECT/CT in patients with a painful postoperative knee and describes typical diagnostic criteria in these patients. Pain after knee surgery is common and is influenced by the underlying pathology, the type of surgery, and the patient. Knee joint-preserving surgery includes osteotomy, ligament reconstruction, meniscus surgery, and cartilage repair procedures, often used in combination. Knee arthroplasty procedures consist of unicondylar, patellofemoral, and primary or revision total knee prosthesis. In patients with pain after knee joint-preserving surgery, MRI remains the reference standard. After ligament reconstruction, CT can evaluate postoperative tunnel positioning, and bone SPECT/CT can contribute by assessing overloading or biodegradation problems. After meniscal or cartilage surgery, SPECT/CT can be particularly helpful to identify compartment overloading or nonhealing chondral or osteochondral lesions as cause of pain. SPECT/CT arthrography can assess cartilage damage at an early stage due to altered biomechanical forces. After corrective osteotomy of the knee, SPECT/CT can reveal complications such as overloading, nonunion, or patellofemoral problems. After arthroplasty, conventional radiographs lack both sensitivity to detect aseptic loosening and specificity in differentiating aseptic from infectious loosening. Secondly, hardware-induced artifacts still hamper CT and MRI, despite improving and increasingly available metal artifact reduction techniques. Bone scintigraphy is a proven useful adjunct to conventional radiography and MRI to reveal the pain generator and is less hampered by artifacts from metallic implants compared with CT and MRI. Nevertheless, the optimal imaging strategy in evaluating complications after knee arthroplasty is still a matter of debate. Although the evidence of the use of BS SPECT/CT is still limited, it is growing steadily. In particular, recent data on specific uptake patterns in tibial and femoral zones after total knee arthroplasty and the impact of integrating biomechanics into the assessment of SPECT/CT appear promising, but more research is needed.

Unicompartmental knee arthroplasty: Current indications, technical issues and results

An age younger than 60 years, a body weight of 180 lb (82 kg) or more, performing heavy work, having chondrocalcinosis and having exposed bone in the patellofemoral (PF) joint are not contraindications for unicompartmental knee arthroplasty (UKA).Severe wear of the lateral facet of the PF joint with bone loss and grooving is a contraindication for UKA.Medial UKA should only be performed in cases of severe osteoarthritis (OA) as shown in pre-operative X-rays, with medial bone-on-bone contact and a medial/lateral ratio of < 20%.The post-operative results of UKA are generally good. Medium-term and long-term studies have reported acceptable results at 10 years, with implant survival greater than 95% for UKAs performed for medial OA or osteonecrosis and for lateral UKA, especially when fixed-bearing implants are used.When all implant-related re-operations are considered, the 10-year survival rate is 94%, and the 15-year survival rate is 91%.Aseptic loosening is the principal failure mechanism in the first few years in mobile-bearing implants, whereas OA progression causes most failures in later years in fixed-bearing implants.The overall complication rate and the comprehensive re-operation rate are comparable in both mobile bearings and fixed bearings.The survival likelihood of the all-polyethylene UKA implant is similar to that of metal-backed modular designs for UKA.Notable cost savings of approximately 50% can be achieved with an outpatient UKA surgery protocol. Outpatient surgery for UKA is efficacious and safe, with satisfactory clinical results thus far. Cite this article: EFORT Open Rev 2018;3:363-373. DOI: 10.1302/2058-5241.3.170048.

Application of different patella height indices in patients undergoing total knee arthroplasty

BACKGROUND

One complication of total knee arthroplasty (TKA) is patella baja (PB). Patellar tendon shortening and joint line elevation are two main causes of PB. The purpose of this study was to determine the incidence of PB before and after TKA by measuring the patellar height and provide evidence for choosing a suitable index.

METHODS

In total, 256 consecutive patients who underwent primary TKA were included in this study. Radiographic measurements were performed; the Insall-Salvati (IS) index, modified IS (MIS) index, Blackburne-Peel (BP) index, and Caton-Deschamps (CD) index were computed; and the incidence of PB was calculated before and after the operation. The consistency between the IS and MIS indices and between the BP and CD indices was analyzed.

RESULTS

The preoperative incidence of true PB (TPB) and pseudo-PB (PPB) was 9.4 and 0.8%, respectively. The postoperative incidence of TPB and PPB was 10.2 and 9.0%, respectively. The consistency between the IS and MIS indices was moderate preoperatively (pre-kappa = 0.602) and postoperatively (post-kappa = 0.742). The consistency between the BP and CD indices was moderate preoperatively (pre-kappa = 0.742) and good postoperatively (post-kappa = 0.797).

CONCLUSION

The incidence of PB, especially PPB, increased after TKA. The CD and BP indices are of greater importance for the diagnosis of PB after TKA. The MIS index is a better choice than the IS index to measure the length of the patellar tendon. To measure the height of the joint line, the BP index is better postoperatively and the CD index is better preoperatively.