The Assessment of Patient Specific Instrumentation for Unicompartmental Knee Replacement

Patient-specific instrumentation guides have previously been used to improving surgical accuracy and ease of implantation during Total Knee Replacement but have received less attention for implanting Unicompartmental Knee Replacement. The aim of this prospective study is to compare the accuracy of implantation and functional outcome of mobile bearing medial Unicompartmental Knee Replacement implanted with and without patient specific instrumentation by experienced knee surgeons.

Study Overview

• Status: Completed
• Conditions: Knee Arthritis
• Intervention / Treatment: Procedure: Patient Specific Instrumentation; Procedure: Conventional Instrumentation

Detailed Description

The aim of this prospective study is to compare the accuracy of implantation and functional outcome of mobile bearing medial Unicompartmental Knee Replacements implanted with and without patient specific instrumentation by experienced Unicompartmental Knee Replacement surgeons.

This single-centre parallel-design trial was conducted between March 2012 and March 2014 at the Nuffield Orthopaedic Centre, Oxford. Four expert knee surgeons performed all of the procedures in this study. Patients who were being placed on the waiting list for a medial Unicompartmental Knee Replacement, and met the entry criteria for the trial, were asked to see if they would be willing to receive further information about participation in the study. They were provided with a study information leaflet that they could read in their own time. A member of the research team subsequently contacted the patients in order to determine if they would agree to take part in the study and enrolled them onto the study.

Patients were randomized to either Patient Specific Instrumentation, or Conventional Instrumentation group. There were 23 patients (23 knees) in the Patient Specific Instrumentation group and 22 patients (22 knees) in the Conventional Instrumentation group. Randomization was performed using sealed opaque envelopes. Concealment from operating surgeons and patients was not possible owing to the surgeon needing to confirm the Patient Specific Instrumentation plans, and the patients undergoing pre-operative MRI scans. Patient Specific Instrumentation group patients underwent an MRI scan using the protocol outlined by the Patient Specific Instrumentation manufacturers to plan development of the Patient Specific Instrumentation guides. The preliminary plan indicating prosthesis size, positioning, alignment, and proposed bone resection levels was reviewed by the surgeons who accepted the default preoperative plans unless gross errors were present. The patient specific cutting blocks were then manufactured and sent for sterilization.

Operative Technique:

All patients received a mobile bearing medial Oxford unicompartmental knee replacement via a minimally invasive approach under general anaesthetic, and high thigh tourniquet. Intra-operatively, the bone cuts were made through the Patient Specific Instrumentation guides without the use of any intra or extra-medullary instrumentation on the femoral side but with a tibial extramedullary guide for some cases. The subsequent milling process and all soft tissue balancing was performed manually in the standard fashion.

Post-operatively, the need to have a blood transfusion, and the change haemoglobin levels were also recorded. Oxygen saturation levels over the first 24 hours post surgery were also recorded. Screened anteroposterior and lateral post-operative radiographs were performed prior to discharge. Patients attended the physiotherapy ward discharge clinic at six weeks. A further clinical review was performed at 12 months at which point Oxford Knee Scores were recorded.

The primary outcome measure was radiological assessment of component positioning. (See Outcome measures section for more detail)

Target sample size:

The sample size was calculated from a previous study that used similar radiological assessments to compare unicompartmental knee replacements performed using conventional instrumentation, with those performed using computer navigation. In this study, the standard deviation of the tibia varus/valgus angle for the control group was 3.6°. Assuming a minimum clinically important difference of 3°, the standard mean difference would be 0.8. Hence with a power of 0.8 and significance level of 0.05, a total sample size of 44 patients (22 in each group) was required.

• Study Type: Interventional
• Enrollment (Actual): 45
• Phase: Not Applicable

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• Both cruciate ligaments functionally intact
• Full thickness cartilage in the lateral compartment
• Correctable intra-articular varus deformity
• Full thickness cartilage loss in the medial compartment

Exclusion Criteria:

• Contra-indication for MRI
• All forms of inflammatory arthritis

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Patient Specific Instrumentation; Patients undergoing unicompartmental knee replacement with the additional aid of patient specific instrumentation.	Procedure: Patient Specific Instrumentation; Patients will undergo a medial unicompartmental knee replacement. This knee replacement is implanted using patient specific cutting guides that have been produced based on the patient's individual anatomy (using plans from pre-operative MRI scans of the patient's knee).
Active Comparator: Conventional Instrumentation; Patients undergoing unicompartmental knee replacement using standard instrumentation.	Procedure: Conventional Instrumentation; Patients will undergo a medial unicompartmental knee replacement using standard conventional instruments.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Radiological Assessment of Component Positioning	Radiological assessment of component positioning and alignment based on post-operative knee radiographs.	Within a weeks after surgery

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Assessment of Functional Outcome	Use of the patient reported outcome tool (Oxford Knee Score) to determine functional outcome at one year following surgery. Total score is 48. Minimum score 0 and Maximum score 48 with higher score indicating better function. Scores on a scale	One year after surgery

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Post-operative Change in Haemoglobin Between Baseline Baseline and 48 Hours After Surgery	Change in haemoglobin levels between baseline and 48 hours after surgery will be determined	Within the first 48 hours after surgery
Number of Participants With The Need for Blood Transfusion Following Surgery	Number of Participants with The Need for Blood Transfusion within 48 hours of Surgery	Within the first 48 hours after surgery

Collaborators and Investigators

• Sponsor: Oxford University Hospitals NHS Trust
• Investigators: Principal Investigator: Andrew Price, FRCS PhD, Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, University of Oxford

Study record dates

Study Major Dates

• Study Start: March 1, 2012
• Primary Completion (Actual): February 1, 2013
• Study Completion (Actual): March 1, 2014

Study Registration Dates

• First Submitted: April 15, 2016
• First Submitted That Met QC Criteria: April 21, 2016
• First Posted (Estimate): April 22, 2016

Study Record Updates

• Last Update Posted (Actual): November 16, 2021
• Last Update Submitted That Met QC Criteria: October 18, 2021
• Last Verified: April 1, 2016

More Information

Terms related to this study

• Keywords: Patient Specific Instrumentation; Unicompartmental Knee Replacement
• Additional Relevant MeSH Terms: Joint Diseases; Musculoskeletal Diseases; Arthritis
• Other Study ID Numbers: 7110

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Plan to publish in high impact peer reviewed orthopaedic journal