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Article
Early results of patellofemoral inlay
resurfacing arthroplasty using the
HemiCap Wave prosthesis
Akash Patel, Zakir Haider, Amarjit Anand,
and Dominic Spicer
Abstract
Background: Common surgical treatment options for isolated patellofemoral osteoarthritis include arthroscopic
procedures, total knee replacement and patellofemoral replacement. The HemiCap Wave patellofemoral resurfacing
prosthesis is a novel inlay design introduced in 2009 with scarce published data on its functional outcomes. We aim to
prospectively evaluate early functional outcomes and complications, for patients undergoing a novel inlay resurfacing
arthroplasty for isolated patellofemoral arthrosis in an independent centre. Methods: From 2010 to 2013, 16 consecutive
patients underwent patellofemoral resurfacing procedures using HemiCap Wave (Arthrosurface Inc., Franklin, Massa-
chusetts, USA) for anterior knee pain with confirmed radiologically and/or arthroscopically isolated severe patellofemoral
arthrosis. Standardized surgical technique, as recommended by the implant manufacturer, was followed. Outcome
measures included range of movement, functional knee scores (Oxford Knee Score (OKS), Knee Injury and Osteoarthritis
Outcome Score (KOOS) and Short Form-36 (SF-36)), radiographic disease progression, revision rates and complications.
Results: Eight men and eight women underwent patellofemoral HemiCap Waveresurfacing, with an average age of 63 years
(range: 46–83). Average follow-up was 24.1 months (6–34). Overall, post-operative scores were excellent. There was a
statistically significant improvement in the post-operative OKS, KOOS and SF-36 scores (p<0.01).Onepatienthad
radiological disease progression. One patient underwent revision for deep infection. Two other minor complications were
observed and treated conservatively. Conclusions: The HemiCap Wave patellofemoral resurfacing prosthesis has
excellent early results in terms of functional outcomes, radiological outcomes and low complication rates. At the very least,
early results show that the HemiCap Wave is comparable to more established onlay prostheses. The HemiCap Wave thus
provides a safe and effective surgical option in the treatment of isolated patellofemoral osteoarthritis in selected patients.
Keywords
arthroplasty, HemiCap Wave, inlay, patellofemoral, resurfacing
Introduction
Patellofemoral arthritis is a significant cause of morbidity
treated by orthopaedic surgeons. It is an increasingly
important issue, now recognized to be more common than
previously thought.
1
Reports suggest that isolated sympto-
matic patellofemoral osteoarthritis occurs between 8%and
13%in patients over the age of 60 years.
2,3
Risk factors for developing patellofemoral osteoarthritis
include trauma, recurrent dislocations, patellofemoral mis-
alignment and trochlear dysplasia.
4
However, often there is
no obvious cause in many patients.
Initial treatment options are conservative and include
weight loss, taping, bracing, physiotherapy, activity mod-
ification and anti-inflammatory medication. Surgical treat-
ment options include procedures to correct patellofemoral
Department of Trauma and Orthopaedic, St Mary’s Hospital, Imperial
College Healthcare NHS Trust, London, UK
Corresponding author:
Zakir Haider, Department of Trauma and Orthopaedic, St Mary’s Hospital,
Imperial College Healthcare NHS Trust, Paddington, London W2 1NY, UK.
Email: zakirhaider10@gmail.com
Journal of Orthopaedic Surgery
25(1) 1–5
ªJournal of Orthopaedic Surgery 2017
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DOI: 10.1177/2309499017692705
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Journal of
Or thopaedic
Surger
y
pathomechanics, arthroscopy (debridement, microfracture
and autologous chondrocyte implantation), total knee
replacement (TKR), patellectomy and patellofemoral
replacement.
Indications for isolated patellofemoral arthroplasty
(PFA) include the following
5
:
1. failure of conservative treatment,
2. absence of tibiofemoral arthritis,
3. normal patella alignment/tracking, and
4. intact/stable menisci and ligaments.
Patellofemoral replacement has been described since
1955, when McKeever performed patellar resurfacing in
40 knees, with initial designs yielding less than satisfactory
results.
6
Patellofemoral joint resurfacing gained further
interest in the 1970s with publication of the results of the
first generation of prostheses.
7
In 1974, Bechtol introduced
both patellar and femoral resurfacing components designed
to be used either in isolation or in conjunction with a uni-
condylar or TKR.
8
Results with first-generation prosthesis
have been variable, with significant improvements in
newer designs.
4,9
The high failure rates reported with some
of the early onlay designs, such as the Lubinus,
10
resulted
in many surgeons preferring TKR for isolated patellofe-
moral arthritis.
11
The HemiCap Wave patellofemoral prosthesis is an
inlay design, intended for patients with isolated patellofe-
moral arthritis and normal patella tracking. This prosthesis
was only introduced in 2009 and little data has been pub-
lished on its functional outcomes. HemiCap Wave is the
only true complete inlay type patellofemoral replacement
(Figure 1). The prosthesis aims to maintain native joint
biomechanics by intraoperative three-dimensional joint
mapping, and the use of contoured implants enables a more
anatomical resurfacing.
12
A biomechanical study assessing
patellofemoral kinematics of the inlay focal HemiCap res-
urfacing demonstrated anatomic re-approximation of the
patellofemoral surface and knee contact pressures.
13
One study evaluated clinical outcomes and sports-
related results in a cohort of 27 patients aged 42 years
(+13) who had undergone HemiCap Wave resurfacing.
Results revealed statistically significant improvements
post-operatively in Western Ontario and McMaster Univer-
sities Osteoarthritis Index (WOMAC), pain visual analogue
scale (VAS) and subjective International Knee Documen-
tation committee (IKDC) scores.
12
Verma et al.
14
published a case series assessing a similar
prosthesis, the focal HemiCap resurfacing. This is a much
smaller inlay design and is used for isolated patellofemoral
focal defects. Forty-three procedures were undertaken and
patients were followed up for a mean of 9 months (range:
1–20). Overall, good post-operative functional results and
surgeon satisfaction were demonstrated.
The aim of this study is to present our early results on
functional outcomes and complications for patients under-
going HemiCap Wave PFA for isolated patellofemoral
arthrosis.
Methods
Sixteen patients were included in this study who underwent
patellofemoral resurfacing using HemiCap Wave (Arthro-
surface Inc., Franklin, Massachusetts, USA) for isolated
patellofemoral arthrosis from March 2010 to July 2013.
No children or vulnerable adult groups were included.
Indications for patellofemoral replacement included
severe isolated patellofemoral osteoarthritis characterized
by anterior knee pain and osteoarthritic changes on radio-
graphs only in the patellofemoral joint with normal tibio-
femoral compartments and normal patella alignment.
Diagnosis of isolated patellofemoral osteoarthritis was
based on clinical, radiological and, where available, arthro-
scopic findings (some patients previously underwent
arthroscopy to assess and debride the patellofemoral joint
(PFJ), specifically any loose patellofemoral chondral
flaps). Patients with any degree of fixed flexion deformities
were excluded.
All patients had preoperative weight-bearing standard
anteroposterior, lateral and patella skyline radiographs.
MRI scanning was also undertaken to confirm normal tibio-
femoral cartilage surfaces and assess PFJ. Surgery was
performed in consecutive patients by the senior author or
under his direct supervision.
Post-operatively, patients were allowed to weight bear
as tolerated and followed a standardized physiotherapy
protocol.
Primary functional outcomes were measured using the
Oxford Knee Score (OKS),
15
Knee Injury and Osteoarthri-
tis Outcome Score (KOOS)
16
and Short Form-36 (SF-36)
17
recorded pre- and post-operatively. The OKS has been used
in multiple studies assessing other PFA designs
11,18,19
and
is a validated patient-reported functional outcome measure.
Use of the OKS allows direct comparison of the Hemi-
Cap Wave resurfacing with other patellofemoral joint
Figure 1. HemiCap Wave (trochlear and patella components).
2Journal of Orthopaedic Surgery 25(1)
replacements, such as the Avon prosthesis (Stryker, How-
medica Osteonics, Allendale, New Jersey, USA). Both the
KOOS and SF-36 are validated and have been highly rec-
ommended in a study by Paxton and Fithian
20
assessing
outcome instruments for PFA.
Secondary outcome measures included range of motion,
radiological parameters (progression of tibiofemoral
osteoarthritis as per Kellgren and Lawrence/Ahlback grad-
ing) as well as complications and reoperations. Data was
prospectively collected using a standardized proforma from
patient notes and Picture Archiving and Collection System
(Philips Medical Systems, Sectra Imtec AB, Sweden).
Patients were routinely followed up in clinic, and post-
operative radiographs were taken. They were reviewed by
the senior surgeon and first author at 6 weeks, 3 months,
6 months and yearly from date of surgery. Range of motion
was measured using a goniometer by the first author only to
aid reliability of measurements. Data was analysed using
SPSS (IBM-SPSS, New York, USA). To test for statistical
significance, paired t-test was used with significance level
set as p< 0.05.
Ethical considerations
This study was conducted as a service evaluation. No fund-
ing/sponsorship from the implant company was obtained to
aid this study. As part of the clinical team caring for these
patients, no consent was required to assess patient notes.
Data was held in accordance with the Data Protection Act.
Approval for this study was obtained from the Biomedical
Research Ethics Sub-committee and regulatory compliance
department at Imperial College London.
Results
Sixteen patients underwent patellofemoral resurfacing
using HemiCap Wave for isolated severe osteoarthritis.
The cohort included eight men and eight women with an
average age of 63 years (46–83) and Body Mass Index 27.2
(22.5–30) at time of surgery. The mean follow-up was 24.1
months (6–34), and no patients were lost to follow-up.
Six patients had previous knee surgery. Of these, five
patients had arthroscopies with debridement of patellofe-
moral chondral defects. Two of these five patients also had
partial meniscectomies. One patient had tibial tubercle
transfer and autologous matrix-induced chondrogenesis.
At operation, all patients had severe patellofemoral
osteoarthritis. Only one patient had grade 1 (Outerbridge)
osteoarthritis in the medial compartment. There were no
intraoperative complications.
Statistically significant improvements were found in
mean scores for the OKS and KOOS post-operatively
(p< 0.01). Although there was significant improvement
in the physical SF-36 post-procedure (p< 0.01), improve-
ments in the mental SF-36 and increase in knee flexion of
5post-procedure were found to be statistically insignifi-
cant (Table 1).
Three patients had post-operative complications. One
patient developed keloid scarring which was asymptomatic
and did not require treatment. One patient developed synovi-
tis which settled with anti-inflammatory medication. A third
patient had continuing pain and swelling post-operatively. He
had persistently raised inflammatory markers with suspected
deep infection. He subsequently underwent a joint aspiration
which was negative with eventual revision to a TKR 18
months after initial surgery for infection.
At follow-up, only one patient had progression of
osteoarthritis. She was 23 months post-surgery with grade
2 (Kellgren and Lawrence) and grade 2 (Ahlback) medial
tibiofemoral compartment osteoarthritis. However, she was
asymptomatic and did not require further intervention.
Discussion
Isolated patellofemoral arthritis is a significant cause of mor-
bidity, which can be treated surgically with PFA. This study
assessed outcomes of the HemiCap Wave patellofemoral
replacement for patients with isolated patellofemoral
osteoarthritis. We assessed 16 patients pre- and post-
operatively and found a statistically significant improvement
in their KOOS, OKS and SF-36 (physical) scores at an aver-
age of 24.1 months follow-up (p< 0.01). Only two minor
complications were observed, neither of which required sur-
gical intervention. These results suggest good short-term
functional outcomes with low complication rates.
To the best of our knowledge, only two studies to date
have evaluated functional outcomes of the HemiCap
Wave.
12,21
Twenty-seven patients were included by Imhoff
et al.
12
with an average age of 42 and were followed up
over 24 months. The patients were split into two groups:
those who underwent isolated patellofemoral inlay
Table 1. Comparison of pre- and post-operative functional outcome measures.
Outcome measure Mean preoperative value Mean post-operative value Statistical significance
Range of movement (knee) 0–1150–120Nil
OKS 19 (2–30) 35 (10–44) p< 0.01
KOOS 39 (5–64) 55 (33–85) p< 0.01
SF-36 (physical) 32 (19–40) 53 (19–70) p< 0.01
SF-36 (mental) 42 (18–55) 45 (20–62) Nil
OKS: Oxford Knee Score; KOOS: Knee Injury and Osteoarthritis Outcome Score; SF: Short Form-36.
Patel et al. 3
surfacing and those who required inlay surfacing and con-
comitant procedures to address patellofemoral instability/
malalignment and tibiofemoral malalignment. Authors
found a statistically significant reduction in total WOMAC,
IKDC and pain VAS scores as well as sports-related Tegner
Score and found more patients partaking in sports post-
operatively. Two patients required reoperation for compo-
nent disassembly and graft slippage post-concomitant med-
ial patellofemoral ligament reconstruction.
Our study is different in terms of the considerably
younger cohort of patients used by Imhoff et al.
12
and some
patients requiring concomitant procedures at time of resur-
facing as well different functional outcomes measures
used. Another paper, published by the implant manufac-
turer (Arthrosurface Press) commentated on a brief inves-
tigation of 22 patients with mean age of 43 years who
underwent HemiCap Wave resurfacing. Follow-up was for
15 months, and preliminary results revealed clinical
improvement in the Kujala and IDKC scores.
22
One study compared an onlay design prosthesis (Jour-
ney PFJ, Smith & Nephew, UK) to the inlay HemiCap
Wave in 15 patients. They found statistically significant
improvements in WOMAC, Lysholm and pain VAS scores
post-operatively with both prostheses. No significant dif-
ference was found in clinical outcome scores between
onlay versus inlay designs. However, in the onlay group,
53%of patients exhibited progression in osteoarthritis
compared to the inlay group (p¼0.009).
Statistics from the 12th annual report (2015) from the
United Kingdom National Joint Registry (NJR) reveal that
PFA makes 1.3%of all primary knee replacements. The
median age for patients undergoing PFA is 59 years com-
pared to 70 years for TKR; hence, survivorship of prosthesis
is all the more important. Between 2003 and 2014, the Avon
prosthesis has been most popular forming 44.8%of all PFA
performed (4457 out of 9945 PFA procedures) followed by
the Femoro Patella Vialli (Wright Medical, UK) with 1433
procedures. In total, there are five PFA prostheses, which
data is provided for by the NJR; all of which have an onlay
design. The Avon prosthesis, however, most closely resem-
bles the HemiCap Wave patellofemoral resurfacing in
terms of engineering. It is the only patellofemoral pros-
thesis with more than 1000 cases having longer than a
5-year follow-up. In terms of survivorship, only three
prostheses had more than a thousand cases available, and
the cumulative percentage probability for a first revision
at 5 years was between 7.66%for Avon and 12.39%for
Journey PFJ (Smith & Nephew). The most common indi-
cation for revision was progression of osteoarthritis.
These results show continued use of traditional onlay
designs however, as more data is collected on the newer
generation of inlay design prostheses such as the Hemi-
Cap Wave; it may reveal a better alternative.
Advantages of inlay resurfacing include preservation
of native geometry with minimal bone loss and soft
tissue disruption, thus causing minimal disruption to
natural joint biomechanics and reducing the risk of joint
overstuffing. The multiple convexities of the HemiCap
Wave assure anatomic fit.
12
Weaknesses of this study include a small sample size
with non-significant mental SF-36 score and range of
motion outcome likely due to this reason. Strengths include
the prospective design with complete pre- and post-
operative scores with no loss to follow-up. This study also
benefits from being a consecutive series performed or
supervised by a single surgeon in an independent centre,
reducing confounders, with strict inclusion criteria.
We recommend further research to be performed using a
randomized controlled study, larger homogenous patient
cohort with longer follow-up. Additionally, future studies
should use similar functional outcome measures to allow
study results to be compared.
Conclusion
In conclusion, little data exists on functional outcomes fol-
lowing use of the HemiCap Wave prosthesis. Our results
demonstrate that the HemiCap Wave has excellent early
results, in terms of functional outcomes, radiological out-
comes and low complication rates. At the very least, early
results show that the HemiCap Wave is comparable to more
established onlay prostheses. The HemiCap Wave thus pro-
vides a safe and effective surgical option in the treatment of
isolated patellofemoral osteoarthritis in selected patients.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The author(s) received no financial support for the research,
authorship, and/or publication of this article.
References
1. Gao X, Xu Z, He R, et al. A preliminary report of patellofe-
moral arthroplasty in isolated patellofemoral arthritis. Chin
Med J 2010; 123(21): 3020–3023.
2. Davies A, Vincent A, Shepstone L, et al. The radiologic pre-
valence of patellofemoral osteoarthritis. Clin Orthop 2002;
402: 206–212.
3. McAlindon T, Snow S, Cooper C, et al. Radiographic patterns
of osteoarthritis of the knee joint in the community: the
importance of the patellofemoral joint. Ann Rheum Dis
1992; 51: 844–849.
4. Lonner J. Patellofemoral arthroplasty. JAmAcadOrthop
Surg 2007; 15: 495–506.
5. Cannon A, Stolley M, Wolf B, et al. Patellofemoral resurfa-
cing arthroplasty: literature review and description of a novel
technique. Iowa Orthop J 2008; 28: 42–48.
6. McKeever D. Patellar prosthesis. J Bone Joint Surg (Am)
1955; 37–A: 1074–1084.
4Journal of Orthopaedic Surgery 25(1)
7. Bazina M, Fox J, Del Pizzio W, et al. Patellofemoral replace-
ment. Clin Orthop 1979; 144: 98–102.
8. Krajca-Radcliffe J and Coker T. Patellofemoral arthroplasty:
A 2- to 18-year follow-up study. Clin Orthop Rel Res 1996;
330: 143–151.
9. Leadbetter W, Ragland P and Mont M. The appropriate use of
patellofemoral arthroplasty: an analysis of reported indica-
tions, contraindications, and failures. Clin Orthop Rel Res.
2005; 436: 91–99.
10. Tauro B, Ackroyd C, Newman J, et al. The Lubinus patello-
femoral arthroplasty: a five- to ten-year prospective study. J
Bone Joint Surg (Br) 2001; 83–B: 696–701.
11. Starks I, Roberts S and White S. The Avon patellofemoral
joint replacement: independent assessment of early functional
outcomes. J Bone Joint Surg (Br) 2009; 91–B: 1579–1582.
12. Imhoff AB, Feucht MJ, Meidinger G, et al. Prospective
evaluation of anatomic patellofemoral inlay resurfacing:
clinical, radiographic, and sports-related results after 24
months. Knee Surg Sports Traumatol Arthrosc 2015;
23(5): 1299–1307.
13. Provencher M, Ghodadra N, Verma N, et al. Patellofemoral
kinematics after limited resurfacing of the trochlea. J Knee
Surg. 2009; 22: 310–316.
14. Verma N, Geissler W, Merwe W, et al. Congruent patellofemoral
resurfacing, part 1: objective multicentre assessment, surgical
technique and case report.Franklin,Massachusetts,USA:
Arthrosurface Press, 2008.
15. Dawson J, Fitzpatrick R, Murray D, et al. Questionnaire on
the perceptions of patients about total knee replacement.
J Bone Joint Surg (Br) 1998; 80–B: 63–69.
16. Roos E, Roos H, Lohmander L, et al. Knee injury and osteoar-
thritis outcome score (KOOS) – development of a self-
administered outcome measures. J Orthop Sports Phys Ther
1998; 28(2): 88–96.
17. Ware J. SF-36 health survey update. Spine. 2000; 25(24):
3130–3139.
18. Ackroyd C, Newman J, Evans R, et al. The Avon patellofe-
moral arthroplasty: five-year survivorship and functional
results. J Bone Joint Surg (Br) 2007; 89–B: 310–315.
19. Odumenya M, Costa M, Parsons N, et al. The Avon
patellofemoral joint replacement: five year results from
an independent centre. J Bone Joint Surg (Br) 2010; 92–
B: 56–60.
20. Paxton E and Fithian D. Outcome instruments for patellofe-
moral arthroplasty. Clin Orthop 2005; 436: 66–70.
21. Feucht M, Cotic M, Beitzel K, et al. A matched-pair compar-
ison of inlay and onlay trochlear designs for patellofemoral
arthroplasty: no differences in clinical outcomes but less pro-
gression of osteoarthritis with inlay designs. Knee Surg
Sports Traumatol Arthrosc 2015; 1–8.
22. Imhoff AB, Schepsis A, Scho¨ttle PB., et al. Review of con-
gruent patellofemoral inlay arthroplasty. From focal to total
patellofemoral surface reconstruction. Franklin, Massachu-
setts, USA: Arthrosurface Press, 2014.
Patel et al. 5