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Abstract

Background:

Medial patellofemoral ligament (MPFL) reconstruction is a common procedure to treat recurrent patellar instability. Outcomes in older patients after this procedure have been less frequently reported in the literature.

Hypothesis:

Patients ≥30 years of age would demonstrate similar subsequent dislocation risk and patient-reported outcomes (PROs) after MPFL reconstruction to younger patients.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A retrospective review was undertaken to identify patients who underwent isolated MPFL reconstruction between 2008 and 2020. Patients were categorized into 2 groups based on age ≥30 years or <30 years at the time of surgery. Subsequent patellar dislocation risk and PROs (Knee injury and Osteoarthritis Outcome Score [KOOS], Norwich score, and Marx activity score) were compared between groups. PROs were compared controlling for anatomic and other demographic differences between groups.

Results:

A total of 228 patients underwent isolated MPFL reconstruction in the study period; 177 patients (78%) were assessed for subsequent patellar dislocation a minimum of 1 year postoperatively (median, 3.4 years). The study included 140 patients <30 years of age at surgery and 37 patients ≥30 years of age at surgery. Subsequent dislocation occurred in 9 patients (5.1%), including 7 patients <30 years (5.0% subsequent dislocation risk) and 2 patients ≥30 years (5.4% subsequent dislocation risk; P > .99). In total, 147 patients completed PRO score surveys at a median of 3.8 years postoperatively. Patients ≥30 years at surgery (n = 31) had poorer KOOS pain (82.1 vs 91.7; P = .03), KOOS activities of daily living (94.1 vs 97.1; P = .04), and Marx activity score (1 vs 7; P < .001) compared with the patients <30 years (n = 116). After adjusting for anatomic and demographic factors, KOOS pain subscale values were significantly poorer for patients ≥30 years (β = −4.3; 95% CI, −8.3 to −0.2; P = .04). No differences in Norwich score or other KOOS subscale values were noted.

Conclusion:

Patients ≥30 years at the time of MPFL reconstruction demonstrate similar subsequent dislocation risk but poorer KOOS pain subscale and Marx activity values than patients <30 years at the time of MPFL reconstruction.

Keywords

patellar instability,patellar dislocation medial patellofemoral ligament (MPFL)MPFL reconstruction age patient-reported outcomes

Patellar dislocations are common knee injuries frequently associated with significant morbidity and reduced activity levels and can lead to recurrent patellar instability.^2,23,30,34 The medial patellofemoral ligament (MPFL) is recognized as the primary soft tissue stabilizer of the patella and is known to commonly be injured in lateral patellar dislocations.^15,24 Patellar dislocations frequently occur in younger, active patients, and even though initial management is typically nonoperative with bracing and physical therapy, the incidence of recurrent instability is relatively high.^12,20,39 In this setting, reconstruction of the MPFL is often performed to stabilize the patella, typically with good outcomes.³²

Recent investigations have attempted to characterize the effects of anatomic and demographic features on outcomes after MPFL reconstruction. Notably, the effect of patient factors such as articular cartilage damage, trochlear dysplasia, patella alta, patellar tracking (J-sign), axial plane deformities, and tibial tubercle–trochlear groove (TT-TG) distance on outcomes have been studied in detail.^14,17,25,31 The effects of technical factors such as femoral tunnel position, patellar fixation type, graft fixation angle, and graft type have also been explored.^{3,13,17,22,26}

Patient age is another factor that has been examined for its potential effect on outcomes of MPFL reconstruction. Recurrent patellar instability and MPFL reconstruction are frequently reported in younger patients, with the peak incidence for patellar dislocations reported between the ages of 14 and 18 years.³⁰ In previous studies, increased age at the time of MPFL reconstruction has been found to correlate with worse outcomes; however, these studies utilized regression analyses or group comparisons with an age cutoff of 18 years.^16,37 There is a paucity of data on outcomes of older patients after MPFL reconstruction, particularly those ≥30 years.

The purpose of this study was to investigate subsequent patellar dislocation risk, activity level, and patient-reported outcomes (PROs) in patients ≥30 years of age at the time of MPFL reconstruction. We hypothesized that patients ≥30 years would demonstrate similar dislocation risk and PROs but lower activity level after MPFL reconstruction compared with younger patients.

Methods

After institutional review board approval, a retrospective chart review was performed that identified patients who underwent MPFL reconstruction between 2008 and 2020. Recurrent patellar instability was the primary operative indication for surgery. Patients were excluded from this study if they underwent concomitant tibial tubercle osteotomy or other bony procedures. Most reconstructions utilized peroneus longus or semitendinosus allografts; a minority used gracilis tendon autografts (Tables 1 and 2). Chart review was utilized to obtain patient history and characteristics, anatomic factors derived from radiographic assessment, and patellofemoral cartilage status at surgery. Demographics included patient age, sex, and body mass index (BMI). Anatomic factors included patellar height assessed using the Caton-Deschamps (CD) index,⁶ TT-TG distance,³³ and trochlear dysplasia assessed using the trochlear sulcus angle.¹ Intraoperatively, any patellofemoral articular cartilage damage was quantified using the International Cartilage Regeneration & Joint Preservation Society grading system.⁵

Table 1

Baseline Demographics and Patient Characteristics^a

	Total (N = 177)	Age at Surgery		P
	Total (N = 177)	<30 y (n = 140)	≥30 y (n = 37)	P
Age, y	23.2 (8.5)	19.7 (4.3)	36.8 (6.6)	.001
Age at 1st dislocation, y	16.4 (5.4)	15.6 (3.9)	21.0 (8.8)	.014
Years from 1st dislocation to surgery	5.6 (7.3)	3.9 (4.1)	14.7 (12.1)	.001
Sex				.039
Female	113 (64)	84 (60)	29 (78)
Male	64 (36)	56 (40)	8 (22)
BMI, kg/m²	27.3 (6.4)	26.9 (6.0)	28.7 (7.5)	.17
>2 previous dislocations				.031
Yes	83 (50)	62 (46)	21 (68)
No	82 (50)	72 (54)	10 (32)
Unknown	12	6	6
Grade ≥2 cartilage damage in PF joint				.003
Yes	116 (66)	84 (60)	32 (86)
No	61 (34)	56 (40)	5 (14)
CD index	1.13 (0.15)	1.13 (0.15)	1.11 (0.18)	.49
TT-TG distance, mm	16.3 (4.8)	16.1 (4.7)	17.4 (5.0)	.24
Sulcus angle	148.9 (11.4)	148.6 (11.8)	149.9 (9.5)	.57
Crossing sign present	67 (38)	60 (43)	7 (19)	.01
ST spur present	18 (10)	14 (10)	4 (11)	>.99
Cartilage treatments
Chondroplasty	104 (59)	79 (56)	25 (68)	.262
Loose-body removal	39 (22)	35 (25)	4 (11)	.076
Microfracture	16 (9)	14 (10)	2 (5)	.54
Graft source				.239
Autograft	34 (19)	24 (17)	10 (27)
Allograft	143 (81)	116 (83)	27 (73)

Data are presented as n (%) or mean (SD). BMI, body mass index; CD, Caton-Deschamps; TT-TG, tibial tubercle–trochlear groove; PF, patellofemoral; ST, supratrochlear.

Table 2

Baseline Demographics and Patient Characteristics of Those With PROs^a

	Total (N = 147)	Age at Surgery		P
	Total (N = 147)	<30 y (n = 116)	≥30 y (n = 31)	P
Age, y	23.2 (8.9)	19.6 (4.3)	37.6 (6.8)	<.001
Age at 1st dislocation, y	16.3 (5.2)	15.5 (3.8)	20.5 (8.8)	<.029
Years from 1st dislocation to surgery	5.5 (7.2)	3.7 (4.0)	16.1 (12.8)	.008
Sex				.035
Female	94 (64)	69 (59)	25 (81)
Male	53 (36)	47 (41)	6 (19)
BMI, kg/m²	27.3 (6.4)	26.9 (6.0)	28.0 (8.0)	.23
>2 previous dislocations				.028
Yes	65 (47)	48 (43)	17 (55)
No	72 (53)	64 (57)	8 (26)
Unknown	10	4	6
Grade ≥2 cartilage damage in PF joint				.019
Yes	97 (66)	71 (61)	26 (84)
No	50 (34)	45 (39)	5 (16)
CD index	1.13 (0.15)	1.13 (0.15)	1.10 (0.18)	.40
TT-TG distance, mm	15.8 (4.7)	15.5 (4.55)	17.4 (5.15)	.12
Sulcus angle	149.6 (11.4)	150.6 (8.49)	149.4 (11.9)	.58
Crossing sign present	63 (43)	56 (48)	7 (23)	.021
ST spur present	13 (9)	10 (9)	3 (10)	>.99
Cartilage treatments
Chondroplasty	92 (63)	70 (60)	22 (71)	.30
Loose-body removal	34 (23)	31 (27)	3 (10)	.055
Microfracture	11 (7)	9 (8)	2 (6)	>.99
Graft source				.192
Autograft	26 (18)	18 (16)	8 (26)
Allograft	121 (82)	98 (84)	23 (74)

Data are presented as n (%) or mean (SD). BMI, body mass index; CD, Caton-Deschamps; TT-TG, tibial tubercle–trochlear groove; PF, patellofemoral; PRO, patient-reported outcome; ST, supratrochlear.

Further chart review was then undertaken to identify subsequent patellar dislocation events. Patients were then contacted via mail, telephone, or email and further queried regarding subsequent patellar dislocations. Patients were asked to complete PROs including the Knee injury and Osteoarthritis Outcome Score (KOOS),^28,29 Norwich Patellar Instability score,³⁵ and the Marx activity score.²¹ Patients with incomplete data were excused from analysis.

Statistical Analysis

Patient characteristics, anatomy, and outcomes were compared based on age at surgery (<30 years vs ≥30 years). PROs were further compared between age groups via regression analyses, adjusting for the following variables selected a priori: sex, BMI, CD index, TT-TG distance, trochlear sulcus angle, number of previous dislocations, and the presence or absence of grade 2 or worse articular cartilage damage.

Continuous variables were assessed for normality using Shapiro-Wilk tests, and central tendencies were described as mean (standard deviation), median (interquartile range), or frequency (percentage) where appropriate. Group comparisons by age at surgery were performed using Fisher exact tests (categorical variables) and T tests or Mann-Whitney U tests (continuous variables based on normality). The effects of age on KOOS subscales and Norwich scores were evaluated using multivariable linear regression modeling. An alpha level of .05 was considered statistically significant. A power analysis demonstrated that a minimum of 29 patients per group were required to detect a clinically relevant 10-point difference in KOOS subscales⁴⁰ with an expected standard deviation of 15 points with 80% power and alpha set to .05. Statistics were conducted in JMP (Version 16; SAS Institute) and G*Power.¹⁰

Results

A total of 278 patients underwent MPFL reconstruction during the study period. After exclusion of 48 patients treated with a concomitant bony procedure and 2 with missing data, 228 patients who underwent isolated MPFL reconstruction in the study period were eligible for inclusion. Subsequent dislocation data at a minimum of 1 year postoperatively were available for 177 patients (78%) (median follow-up, 3.4 years) (Figure 1). The study included 140 patients <30 years of age at surgery and 37 patients ≥30 years of age at surgery. Patients ≥30 years were more likely to be female and have >2 previous patellar dislocations and demonstrated more articular cartilage damage than the younger group (Table 1). Subsequent patellar dislocations occurred in 9 patients (5.1%), including 7 patients <30 years (5.0% subsequent dislocation risk) and 2 patients ≥30 years (5.4% subsequent dislocation risk) (P > .99).

Figure 1.

Study flow diagram. KOOS, Knee injury and Osteoarthritis Outcome Score; MPFL, medial patellofemoral ligament.

A total of 147 patients completed the KOOS, Norwich, and Marx activity surveys with a median follow-up of 3.8 years. Patients ≥30 years were more likely to be female and have >2 previous patellar dislocations and demonstrated more articular cartilage damage than the younger group (Table 2).

The overall mean KOOS subscale values at follow-up were 89.1 (symptoms), 91.7 (pain), 97.0 (activities of daily living), 85.0 (sport) and 75.0 (quality of life). The overall mean Norwich Patellar Instability score was 8.7, and the Marx activity score was 5. The KOOS pain and activities of daily living subscale values and Marx activity level were lower in patients ≥30 years at the time of surgery, while other PROs were not different between the 2 groups (Table 3).

Table 3

Outcomes of MPFL Reconstruction Based on Age at Surgery (30-Year Cutoff)^a

	Total (N =14 7)	Age at Surgery		P
	Total (N =14 7)	<30 y (n = 116)	≥30 y (n = 31)	P
KOOS values
Symptoms and stiffness	89.1 (25.4)	89.3 (22.5)	85.7 (31.8)	.74
Pain	91.7 (22.2)	91.7 (18.7)	82.1 (50.5)	.034
ADL/function	97.0 (10.3)	97.1 (8.8)	94.1 (23.5)	.042
Sport	85.0 (35.0)	85.0 (35.0)	82.5 (36.3)	.94
QoL	75.0 (31.6)	75.0 (25.8)	75.0 (34.4)	.24
Norwich Patellar Instability score	8.7 (25.3)	7.2 (23.5)	13.7 (27.3)	.12
Marx activity score	5 (10)	7 (8)	1 (6)	<.001

Data are presented as mean (SD). ADL, activities of daily living; KOOS, Knee injury and Osteoarthritis Outcome Score; MPFL, medial patellofemoral ligament; QoL, quality of life.

Multivariable linear regression modeling of KOOS and Norwich values demonstrated age ≥30 years to be associated with a lower KOOS pain subscale value (β = −4.3; 95% CI, −8.3 to −0.2; P = .038) adjusting for sex, BMI, CD index, TT-TG distance, sulcus angle, number of previous dislocations (≤2 vs >2), and the presence or absence of grade ≥2 cartilage damage. Age ≥30 years at surgery was not associated with differences in other KOOS subscales or Norwich score (Table 4).

Table 4

Effect of Age ≥30 Years at the Time of MPFL Reconstruction on PROs via Multivariable Linear Regression Analysis^a

	β-Estimate	Standard Error	95% CI	P
KOOS values
Symptoms and Stiffness	−0.32	2.16	−4.61 to 3.96	.88
Pain	−4.25	2.02	−8.25 to −0.24	.038
ADL/function	−0.92	1.46	−3.81 to 1.98	.53
Sport	1.09	2.94	−4.74 to 6.97	.71
QoL	−4.31	2.97	−10.21 to 1.59	.15
Norwich Patellar Instability score	0.34	2.98	−5.58 to 6.27	.91

ADL, activities of daily living; CD, Caton-Deschamps; KOOS, Knee injury and Osteoarthritis Outcome Score; MPFL, medial patellofemoral ligament; PRO, patient-reported outcome; QoL, quality of life; TT-TG, tibial tubercle–trochlear groove.

Exploration of outcomes of the relatively few (n = 9) patients ≥40 years who underwent MPFL reconstruction did not demonstrate markedly poorer PROs in this population (Table 5). The low number of patients >40 years precluded meaningful statistical analysis of this group.

Table 5

Outcomes of MPFL Reconstruction in Patients Aged ≥40 Years^a

	Age at Surgery ≥40 y (n = 9)
KOOS values
Symptoms and stiffness	95.4 (14.3)
Pain	88.3 (54.3)
ADL/function	97.1 (21.3)
Sport	90.0 (60.0)
QoL	75.0 (42.8)
Norwich Patellar Instability score	10.8 (16.4)
Marx activity score	0 (3)

Data are presented as mean (SD). ADL, activities of daily living; KOOS, Knee injury and Osteoarthritis Outcome Score; MPFL, medial patellofemoral ligament; QoL, quality of life.

Discussion

The most important finding of this study is that age ≥30 years at the time of MPFL reconstruction resulted in similar re-dislocation risk to that of patients <30 years, but poorer KOOS pain scores and Marx activity level were noted in the older group. The difference in KOOS pain subscale values was relatively small (4.3 points) when controlling for other differences between groups, but still evident. This observed increase in knee pain after MPFL reconstruction in relatively older patients in this population is likely multifactorial. The overall sequelae of cartilage degeneration secondary to both trauma and aging is known to induce knee pain and may be driving these findings, as a larger degree of patellofemoral chondral damage was identified in the older cohort.^4,11 While the extent of patellofemoral damage was adjusted for in our analysis and theoretically dampened via adjuvant cartilage procedures at the time of surgery, it may still be influencing these results. Obesity is also well established in its link to knee osteoarthritis,²⁷ and while we did see an increase in mean BMI in older patients, the difference was nonsignificant. Furthermore, decreases in muscle mass and joint stability associated with aging may additionally be contributing to increased pain. Overall, this finding, while statistically significant and warranting further investigation, may not be as clinically important given its relative magnitude to the overall PROs recorded.

The largest and most consistent difference between the 2 groups in this study was in activity level as measured with the Marx scale. Mean activity levels were reduced in older patients compared with younger ones, but with a large interquartile range, suggesting wide variability between individuals. This reduction in the Marx score indicates that older patients were engaging in fewer activities potentially demanding of patellar stability and comfort. It is highly likely that these results are also strongly influenced by the changes in activity type and durations evident as patients age. Achieving a high Marx score requires frequent participation in twisting and pivoting sports. It is possible for patients to be highly active but still score low, such as in swimming, cycling, and some forms of weight training.²¹

Activity level plays a complex role in influencing PROs after ligamentous knee surgery. Reduced activity (particularly participation in twisting and pivoting sports) is likely due to a confluence of physical, psychosocial, and occupational factors. Knee symptoms such as those assessed with the KOOS can contribute to this decline in activity. Interestingly, lower activity level and decreased knee demand may favorably improve patients’ perceptions of knee function and symptoms. Other authors have noted this phenomenon after anterior cruciate ligament reconstruction, with 10-year KOOS values being very similar to KOOS values reported at the 2- and 6-year time points despite steadily decreasing Marx activity levels.³⁶ Lower demands secondary to these lower activity levels may have a role in the generally similar PROs observed between groups in this study.

The small group of patients in this cohort ≥40 years demonstrated comparable KOOS subscale values to younger patients but, again, further decreases in activity level. This finding again highlights the interdependence of KOOS values and activity level. A cohort with a larger number of patients age ≥40 years is needed to more completely evaluate the outcomes of MPFL reconstruction in this age group.

Aside from the small decrease in KOOS pain subscale values, patients ≥30 years of age exhibited generally positive outcomes and similar rates of recurrent dislocation when compared with the younger cohort after MPFL reconstruction. Other orthopaedic ligamentous knee surgeries have demonstrated similarly good outcomes in older patients. Anterior cruciate ligament reconstruction surgery, another procedure routinely done in younger, active individuals but also performed in older patients, has been shown to be a safe and effective procedure with similar outcomes to those of younger cohorts.^7-9 Good outcomes after ligamentous reconstruction have also been demonstrated in older patients treated for multiligament knee injuries. A recent investigation of 12 patients aged ≥40 years demonstrated a high level of satisfaction and adequate PROs 2 years after surgery.³⁸ In a larger cohort, Levy et al¹⁸ also demonstrated the efficacy of multiligament reconstruction in older patients but did note inferior clinical and functional outcomes in patients ≥30 years of age compared with younger patients.

This study adds to the literature by identifying specific impairments in overall postoperative knee function aside from recurrent instability in older patients who underwent MPFL reconstruction. Few previous publications have examined the effect of age on clinical outcomes after MPFL surgery. Lind et al¹⁹ compared outcomes of isolated MPFL reconstruction in 20 children aged 8 to 16 years compared with 179 adults, reporting no evidence of differences in Kujala or pain scales between age groups. However, no explicit comparative statistics were performed between these groups, and the median age of the adult cohort included was only 23 years. Hiemstra and Kerslake¹⁶ used regression analyses of a cohort of 328 MPFL reconstructions (mean age, 24.5 years) to identify poorer scores on patient-reported quality of life measurements associated with 10-year increases in age at the time of surgery, at both 12- and 24-month postoperative time points. The main outcome of this study was the development of a patellofemoral instability instrument to assess disease-specific quality of life. While this instrument included data on pain, it also included other factors, and subscores are not reported. It is unclear if pain, other factors, or a combination were driving these findings. The authors posit a confluence of possible factors ranging from emotional, social, and physical symptoms to functional abilities impacting quality of life scores. Our study expands on these findings by identifying specifically increased pain in the older patients after MPFL reconstruction.

Limitations

One limitation of this analysis was the absence of preoperative scores in patients before MPFL reconstruction. This limitation is important as it limits the ability to determine how much improvement in scores was achieved by patients in different age groups. Additionally, while the median follow-up time was >3 years, the minimum follow-up was only 1 year. This length of follow-up precludes comment on the long-term outcomes of MPFL reconstruction in older patients. Furthermore, there is some loss to follow-up in this cohort. While recurrent dislocation data were available for 78% of patients, PROs were only completed by 64% of the initial cohort, increasing the risk of selection bias. Furthermore, the differences in PROs noted between patients in different age groups could be confounded by known and unknown differences between the groups other than age. Many of these potential confounding variables were controlled for in the multiple regression analyses, but others may still exist. Furthermore, even variables for which adjustments were made could still affect outcomes as such analyses are limited. For example, while the analysis did adjust for differences in cartilage damage between the groups based on the most severe grade of damage present, differences in lesion size and location or other differences may still exist between the groups and affect results. Lastly, this analysis focused on outcomes of patients undergoing isolated MPFL reconstruction. The effect of age on outcomes of patellofemoral surgery that included bony procedures such as tibial tubercle osteotomy remains unknown.

Conclusion

Patients ≥30 years of age at the time of MPFL reconstruction demonstrated similar re-dislocation rates but poorer KOOS pain subscale and Marx activity values at 3.4 years postoperatively than patients <30 years of age at the time of MPFL reconstruction.

Footnotes

Final revision submitted October 8, 2024; accepted November 12, 2024.

One or more of the authors has declared the following potential conflict of interest or source of funding: D.C.F. has received consulting fees from Linvatec, Medical Device Business Services, Smith & Nephew, Vericel, DePuy Synthes Products, Bioventus, and Zimmer Biomet Holdings; nonconsulting fees from Linvatec, Smith & Nephew, Vericel, KARL STORZ Endoscopy–America, Pacira Pharmaceuticals, and Trice Medical; and honoraria from Vericel. C.C.K. has received consulting fees and travel payments from Arthrex. R.A.M. has received a grant from DJO. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Ethical approval for this study was obtained from the Biomedical Institutional Review Board of The Ohio State University (2015H0446, 2/1/16)

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Does Patient Age Matter for Medial Patellofemoral Ligament Reconstruction? Patients ≥30 Years of Age Compared With Younger Patients

Abstract

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Methods

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Results

Discussion

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