Challenges in PKA

Challenges in partial knee arthroplasty  48, 52-57

  • Can be a demanding procedure, with restricted visual field
  • Potential for technical errors
  • Poorly implanted PKA may fail earlier

Successful clinical outcomes following unicompartmental knee arthroplasty (UKA) are dependent on accurate component positioning,56 soft tissue balance and overall limb alignment.54

Source (from 2015)
Manual PKA Revision rate
Australian Registry52
4.8%
Swedish Registry53
4.5%

Surgical experience

Improved accuracy of component positioning with robotic-assisted unicompartmental knee arthroplasty: data from a prospective, randomized controlled study59

Methodology

  • Initial results of 139 patients from the prospective, single center, level I, blinded, randomized controlled trial (RCT) between Mako Partial Knee and manually implanted Biomet Oxford
  • Post-operative CT protocol was performed at three months to assess the accuracy of the planned vs. achieved component positioning in the axial, coronal, and sagittal planes

Results

  • Mako Partial Knee showed more accurate delivery of the surgical plan in all alignment measures, with statistical significance (p‹0.01) for all six parameters:
    • Femur flexion/extension (sagittal)
    • Femur varus/valgus (coronal)
    • Femur internal/external rotation (axial)
    • Tibia flexion/extension (sagittal)
    • Tibia internal/external rotation (axial)
    • Tibia varus/valgus (coronal)
  • The proportion of patients with component implantation within 2˚of target was significantly greater (p‹0.05) in Mako Partial Knee cases compared with the manual cohort for five out of the six parameters (femoral-sagittal, coronal, and axial, tibia- sagittal and axial).

Patient outcomes

Methodology

  • 1007 eligible patients (1135 knees) received a robotic-arm assisted medial UKA (Mako MCK)
  • 797 patients (909 knees) enrolled in a study for 2-year follow up, and were asked a series of questions to determine implant survivorship and satisfaction
  • 164 patients completed the survey at 5-year follow up (study on going)

Results

  • 2-Year follow up
    • 1.2% revision rate
    • 92% patient satisfaction (“Very Satisfied” or “Satisfied”)
  • 5-Year follow up
    • 89.6% patient satisfaction (“Very Satisfied” or “Satisfied”)
Partial Knee Clinical Evidence
Partial Knee Clinical Evidence
Source (from 2015)
Revision rate
Australian Registry52 (manual PKA)
4.8%
Swedish Registry53(manual PKA)
4.5%
Current study60 (robotic PKA)
1.2%

Methodology

  • Initial results of 139 patients from the prospective, single center, level I, blinded, randomized controlled trial (RCT) between Mako Partial Knee and Biomet Oxford
  • Visual Analog Pain Score (VAS) was collected for Mako Partial Knee and Manual Surgery at 90 days post-operative
  • Knee Society Scores were evaluated at 90 days post-operative

Early Results

  • Mako Partial Knee patients reported significantly lower post-operative pain compared to manual patients from Day one to Week eight
  • Almost twice as many Mako Partial Knee patients scored in the “excellent” category of the American Knee Society Scores (AKSS) at 90 days post-operative (57% vs 31% manual surgery)
Partial Knee Clinical Evidence
Partial Knee Clinical Evidence

Methodology

  • 130 patients were included in this prospective cohort study (65 robotic-arm assisted medial UKA, 65 manual TKA)
    • UKA: Mako MCK Medial Onlay
    • TKA: Biomet Vanguard Complete Total Knee utilizing patient-specific cutting jigs based on pre-operative CT
  • Patients were asked to complete the Forgotten Joint Score (FJS) and other PRO (patient-reported outcome) tools at one year and two years follow-up

Results

  • The average FJS was significantly higher for robotic-arm assisted UKA than manual TKA at one year follow-up (p=0.002) and two year follow-up (p=0.004)

Forgotten Joint Score one and two years following surgery. Note that the medial UKA group showed significantly higher scores at one- and two-year follow-up (FJS one year 73.9 +/- 22.8, FJS two year 74.3 +/-24.8) in contrast to the TKA group (FJS one year 59.3 +/- 29.5, p=0.002, FJS two year 59.8 +/- 31.5, p=0.004).

Methodology

  • Twenty seven knees (eighteen TKA, nine robotic-arm assisted UKA) were performed by two surgeons
  • Each patient received a uniform physical therapy (PT) regimen
  • The number of PT visits to reach functional goals was recorded for robotic-arm assisted UKA and manual TKA for the following criteria:
    • Range of motion from five to 115º
    • Recovery of flexion and extension strength to four-fifths of pre-operative strength
    • 250 feet of gait with minimal limp and without an assistive device
    • Ability to ascend and descend a flight of stairs with step over gait and good control

Results

  • Results showed less physical therapy was required for Mako Partial Knee patients compared with manual TKA patients to reach the same functional goals for all five criteria
  • Significant differences (p‹0.05) were seen in minimal limp, flexion to flexion of 115° and extension of 5°

Mako partial knee economics

Effect of age on cost-effectiveness of UKA compared with TKA in the US65

Methodology

  • Markov model constructed using UKA and TKA data from Swedish Knee Arthroplasty Registry, published literature, HCUP government database, and HSS registry
  • Assumption: UKA and TKA experience same post-operative increase in quality of life

Key Results

  • In patients ›65, UKA was dominant over TKA primarily due to higher rehab costs of TKA, even with higher UKA revision rates
  • UKA will become dominant in younger patients if UKA shows an improved QOL and reduced revision rate

Continuum of care

Methodology

  • 110 patients (113 Knees) medial UKA
  • Pre- and post-op radiographs used to measure:
    • Arthritic changes of PFJ graded using Modified Altman Scale
    • Congruence measured on merchant views

Key Results

  • Mechanical lower limb alignment was corrected from 7.69 (SD ±3.58) of varus angle pre-op to 2.95 (SD ±2.65) of varus post-op (P‹ 0.0001)
  • The patellar congruence angle was improved from 14.23 (SD ± 11.22) to 10.05 (SD ± 10.28), postoperatively (P = 0.0038)
  • Pre-operative PFJ congruence and degenerative changes did not affect UKA clinical outcomes. This finding may be explained by the post-op PFJ congruence improvement
Partial Knee Clinical Evidence

Pre-operative Merchant view of a left knee. The trochlear angle (red angle) is 140°. The congruence angle (yellow angle) is 14°. The medial patella–femoral joint space is represented by the purple line.66

Partial Knee Clinical Evidence

Post-operative Merchant view of a left knee. The trochlear angle (red angle) is 140°. The post-operative congruence angle (yellow angle: 6°) is decreased compared to the preoperative one (Fig 3). Moreover, the medial patella–femoral joint space (purple line) is increased by 1.5mm following unicondylar knee arthroplasty.66

Methodology

  • Pre- and post-operative weight bearing radiographs of 47 patients (53 knees) who underwent lateral UKA
  • Congruence Index (CI) was evaluated using an Interactive Closest Point (ICP) algorithm
  • Joint Space Width (JSW) was measured on 3 sites
  • Control group: CI and JSW of the medial compartment in 41 healthy subjects

Key Results

  • The mean CI of knees following lateral UKA significantly improved from 0.92 (SD 0.06) pre-operatively to 0.96 (SD 0.02) (p ‹ 0.001) six weeks post-operatively
  • Post-operatively, the mean inner JSW increased (p = 0.006) and the outer decreased (p = 0.002). The JSW was restored post-operatively as no significant differences were noted in all three locations compared with the control group (inner JSW p = 0.43; middle JSW p = 0.019, outer JSW p = 0.51)
  • Potential prevention or delay of the osteoarthritic progression and restoration of load distribution of medial compartment
Partial Knee Clinical Evidence
Partial Knee Clinical Evidence